Adopting 4 year old with mild-moderate Autism

First I would recommend doing as much research into Autism as you can. Our family has dealt with it on multiple levels (mild to severe). Some of the behaviors you are describing such as lack of conversation skills, social skills, etc. These are not things that you can fix, this is normal for autism. If you are seeking to adopt these children there are a lot of things that you may need to be willing to accept, one being that he will not truly function like a "normal" child and may always need you for support on some level. Imaginative play is most likely not going to happen, and if it does it will be on his terms and the way he wants. The mimicking is normal as well it is called echolalia and it is a way that autistic children process information and relay that information back to you. He may never start a real conversation but he can understand you so please be careful what you say to and about him in his presence. Twirling is sensory activity and it can be soothing for him, he will not play like other children so try not to force him to conform or that will cause more of a problem than you want or need. Making friends will never be in the traditional sense like most children make friends. He may play along side other children but he may not engage with them directly and if he does he may not have the same level of interest in their activities as they would like. Check and see if your school district has a school that knows how to deal with Autism or has a special needs preschool program. This will insure that he is in a smaller group and is able to focus on his skills. Even if he is able to mainstream into a regular classroom he may need an aid to assist him in staying focused or calm during stressful situations in class. Be patient and again do your homework, make sure this is something that you can handle for the rest of your life.