Hi OP, i’m a LSA in early years and if you have a child with an EHCP starting in reception at school it will be likely your child will be appointed someone like me for part of the school week to help him on a one to one basis.
I have worked with children that age with a variety of different needs and doesn’t mean your child is particularly ‘severe’ but that your preschool is adept observing indicators of autism.
So when your child starts reception, hopefully he will be allocated a LSA who strives to pay complete attention to your child to observe and help and provide feedback to the teacher and SENDCO.
On a typical day I will take my child outside for a walk and a decompress when he gets overwhelmed or showing signs of stress, talk to him about his weekend and his interests and then find out what he is fascinated by at the moment and then incorporate that into some learning based activities.
So, if he is into dinosaurs then I can print off a dinosaur themed numbers game to play together, or get some mini dinosaur models to hide in the sand and encourage him to use tongs to pick them out to strengthen fine motor skills, and find dinosaur books/puzzles etc
If he is shy I will bring one child to play a game with us, gradually increasing time with different children then into group games. If he has difficulty concentrating, I will use a timer to explain we are working together on something for 1 minute and increase the time over the year.
If he is upset, I will try to understand why and how to help (flash cards, a walk, a stress ball, a quiet place) If he is angry we will walk it out, talk it out, cry it out or laugh it out.
If he misses you we will talk about you, draw pictures of you, make a card for you and find other things to do that he likes til he can see you again.
I hope this gives some reassurance, OP, that the EHCP can help open doors to a positive transition for your son into school and to be well supported.