OT comes under regulation 6(1)(h). It depends on DS’s needs but that can also cover SALT, physio, clinical psychologist.
Be aware, the summer holidays is one of the exceptions to the timescales when the LA request information from the school during the period it is closed (starting 1 week before closer and finishing 1 week before reopening) and it isn’t practicable for the LA to comply.
For social care assessments, this booklet is helpful.
More generally, it can help to make a timeline of events/any previous assessments, etc. Also think about making notes on things like developmental history, needs/difficulties, likes/dislikes/what makes DS happy, what support is already in place, what has previously been tried, what worked/didn’t work, what is needed but unable to be delivered, what is important to DS/you and what is important for DS, how DS communicates/how others communicate with him, aspirations, what you think DS needs, a bit about family/any other important people in DS’s life.
It can also help to write a list of questions to ask the professional such as what assessments will be undertaken, what observations will be done (e.g. structured and unstructured times, with peers, with adults), will they meet with DS 1:1, how long they will spend with DS. Ask if they will make recommendations for the need for further assessments where they believe they are necessary - sometimes they do and sometimes they don’t.
Finish by asking them to ensure the report is detailed, specified and quantified and requesting the report is sent to you at the same time as it is sent to the LA - you may receive push back on this, but if you request it, it should be done.