Psychiatrist or developmental pediatrician. Not general pediatrician unless he's been on the same meds for a long time and you are confident they won't need to change.

I don't know the answer to your question, by I hear that wait-lists for child psychiatrists are long so maybe reach out to some and get on the list in case you need it for whatever reason? The following practices have been recommended to us:
Healthy Foundations Group
The Chesapeake Center
Dr. Michelle Seelman

My child currently takes Ritalin and Zoloft. We are moving to the DC metro area from overseas and need to find a healthcare provider to continue to prescribe and monitor our child's medication. Do we need pediatric psychiatrist for this or a pediatrician? The healthcare system where we live is different from the US system. Any recommendations of particular doctors are most welcome too. Thank you for the advice.