Experience with special needs child?

We are a family of 4 and live in The Netherlands, and have been asked whether we would consider moving to the Bay Area (in/around Santa Clara, CA) on a 2 year temporary international assignment. Our youngest son is diagnosed with Phelan-McDermid Syndrome and we have another boy who just turned 6. Our youngest son's mental and physical development is significantly delayed (for example: walking just before turning 2 years, at age of 3 only speaking in 1 syllable words) and he requires continuous stimulation and monitoring on his development. We are hoping for advice on how to secure that our youngest son receives the education/support he deserves. We are trying to find out how to secure a good special needs (pre-)school for Sem, where he feels at ease, his development is stimulated and where he can learn English. We are not familiar with the (pre-)schools and regulations for special needs children in the U.S., but the way we understand it now, there is a special education department of the school district has a key role in this process, therefore we hope you can help us with this important topic, which is very close to our heart. Is anybody aware of any schools that could fulfill this important role? We understand that the school district plays an important role in specifying the school and special support for children. Does anybody perhaps have any experience with this process? Did it feel like a collaboration, or was it more like a struggle to get it arranged? Thanking you already very much for your help!