We have been there my son started daycare at 21 months and a month later he was diagnosed with autism. We had a teacher aide who was with him so helped him with anything like sitting on the mat doing some one on one and taking the child away if it gets all too much. He was at daycare until he started school and learnt being around other kids/adults for his social skills.
He was on a gluten free diet in his younger days and that helped with his behaviour. He also gets multi-vitamin, fish oil and vitamin C to help him to be more focus.
He is now 7.5 and in a mainstream school and is doing very well. He does have a teacher aide and does some one on one with him with work that he has to do.