Expert Pediatric Care for Pomona Valley Families
When you bring your child to Pomona Pediatrics, you’re not walking into a practice that’s still figuring things out. You’re walking into a team of seven board-certified pediatricians with decades of experience caring for families across Pomona, Diamond Bar, Claremont, La Verne, San Dimas, Fontana, Rancho Cucamonga, and the surrounding Pomona and San Gabriel Valleys, including communities above and below the 210.
A Practice with Deep Roots
Pomona Pediatrics has been part of this community since the late 1940s, when Dr. John Wilcox founded the practice. Dr. Richard Mabie joined him in 1961 and went on to serve families here for 40 years before retiring in 2000. Dr. Frederick Lauppe joined in 1973 and practiced until 2010. Together, these physicians built something rare: a pediatric practice so trusted that children who were once patients here grew up to become its doctors.
Dr. Sandra Hollenberg, who was once a patient herself, joined the practice in 1982, becoming one of its most dedicated physicians. Dr. Carrie Knoll has a similar story, having been seen here as a child before joining the team in 1998. That kind of continuity happens when a practice genuinely becomes part of the fabric of a community.
Meet Our Pomona Pediatricians
Every physician at Pomona Pediatrics is board-certified in pediatrics and a Fellow of the American Academy of Pediatrics. Together, they bring a combined depth of experience and specialization that families across the Pomona Valley rely on. Most of our doctors live right here in Claremont and the surrounding communities. These aren’t just your children’s physicians; they’re your neighbors.
Sandra Hollenberg, MD (retired)
Dr. Hollenberg has been a cornerstone of Pomona Pediatrics since 1982. Over more than four decades, she has been instrumental in modernizing the practice — championing electronic health records and integrated care systems that have made care more seamless for thousands of families. Retiring in June 2026, she leaves behind a legacy of excellence and deep community commitment.
Carrie Knoll, MD
Dr. Knoll joined Pomona Pediatrics in 1998, continuing a connection to this practice that began in her own childhood. She is board-certified in pediatrics and a fellow of the American Academy of Pediatrics.
James Warren, MD
Dr. Warren joined Pomona Pediatrics in 2001 and has become well respected by generations of families in the community. He is board-certified in pediatrics and a Fellow of the American Academy of Pediatrics, bringing over two decades of experience caring for infants, children, and adolescents across the Pomona Valley.
Ericka Hong, MD
Dr. Hong joined Pomona Pediatrics in 2006. She is board-certified in pediatrics and a Fellow of the American Academy of Pediatrics, with a warm, patient-centered approach that families throughout Pomona and the surrounding communities have come to trust.
Toya Tillis, MD
Dr. Tillis joined Pomona Pediatrics in 2011. She is board-certified in pediatrics and a Fellow of the American Academy of Pediatrics, dedicated to providing compassionate, high-quality care for every child she sees.
Diana Yu, DO
Dr. Yu joined Pomona Pediatrics in 2021. She is board-certified in pediatrics and a Fellow of the American Academy of Pediatrics, bringing a fresh perspective and a deep commitment to family-centered care to our growing team.
Patricia F. Villegas, DO
Dr. Villegas has been practicing since 2019 and joined Pomona Pediatrics in 2024. Board-certified in pediatrics and a Fellow of the American Academy of Pediatrics, she brings a particularly personal perspective to her work: as a mother of two children herself, she approaches every family with empathy and attentiveness that goes beyond clinical training.
Hospital Connection and Specialist Access
We are proudly in close connection with the Pomona Valley Hospital Medical Center, a long-standing affiliation we maintain because of its high-quality inpatient pediatric care, dedicated inpatient pediatric specialists, and excellent neonatology unit. When your child needs hospital-level care, that relationship matters.
Our partnership with Rady Children’s Health (formerly CHOC) also gives our families direct access to Rady’s 24/7 nurse line. This means you have real pediatric guidance available around the clock, even when our office is closed.
And because we’ve been part of this community for over 75 years, we’ve built lasting relationships with trusted local specialists across many fields. When your child needs a referral, we’re not handing you a name from a directory. We’re connecting you with colleagues we’ve worked alongside for decades.
Access That Works for Busy Families
We’ve built our practice around making care accessible, because we know that getting your child seen quickly shouldn’t be a struggle.
Same-day urgent appointments are available by calling between 8:15 and 9:00 a.m. Telephone medical advice is available throughout office hours for established patients. When our office is closed, an on-call physician is always reachable for pressing concerns. And through our Rady Children’s Health partnership, a 24/7 nurse line is available to your family at any hour.
For New and Expecting Parents
Choosing a pediatrician before your baby arrives is one of the best decisions you can make. We invite expecting parents to call our office to schedule a prenatal “get acquainted” visit. This gives you a chance to meet our physicians, ask your questions, and feel confident about the team that will be there from your child’s very first hours.
Once you’ve chosen Pomona Pediatrics and you’re admitted to the hospital for delivery, please let the hospital staff know. One of our physicians will visit you while you’re there and provide guidance on scheduling your newborn’s first appointment.
Our Promise to Every Family
These are the standards we hold ourselves to every single day:
- To make your child’s health our number one priority
- To remain knowledgeable and current in pediatric medicine
- To maintain a clean, welcoming, and professional office environment
- To promote health and well-being in our community
- To listen to your concerns and treat you with respect
Our Mission
Our mission is to help children reach their highest potential by working with parents to promote and maintain their child’s physical and emotional well-being from birth through young adulthood. We are committed to:
- Providing quality, personalized, child-centered care for every patient we serve
- Listening to our patients and their families who we are privileged to serve
- Guiding every child along a path of optimal health and wellness
- Maintaining the highest standards of excellence in pediatric medicine
- Being a trusted resource and partner for families across the Pomona Valley
Our Philosophy
We believe that preventive care and education are the keys to keeping your children healthy. Regularly scheduled well-child visits allow us to assess growth, nutrition, and development and discuss age-appropriate anticipatory guidance. Vaccines are administered per AAP guidelines.
We encourage families to let us know of any change or concern in their child’s medical, family, or environmental history that might impact their health, because the more we know, the better we can care for your child.
As your pediatricians, we believe that caring for children goes far beyond illness care. It includes nutrition, parenting, discipline, school challenges, and adolescent transition. At every stage, we hope to be your family’s most trusted source of medical guidance.
