If you want DS to attend full time, he can unless the school is formally suspending him. You have the choice to send DS part time until the term after he is compulsory school age, or not at all until the term after he is CSA or the beginning of the summer term, whichever comes later but 2.17 of the School Admissions Code (which you can see here) makes it clear it is the parents’ choice:
“Admission authorities must provide for the admission of all children in the September following their fourth birthday. The authority must make it clear in their arrangements that where they have offered a child a place at a school:
a) that child is entitled to a full-time place in the September following their fourth birthday;
b) the child’s parents can defer the date their child is admitted to the school until later in the school year but not beyond the point at which they reach compulsory school age and not beyond the beginning of the final term of the school year for which it was made; and
c) where the parents wish, children may attend part-time until later in the school year but not beyond the point at which they reach compulsory school age.”
You may also find the school suspension and exclusion guidance helpful https://assets.publishing.service.gov.uk/media/6a63426d9a419980593b2b80/suspension-and-permanent-exclusion-from-maintained-schools-academies-and-pupil-referral-units-in-England-including-pupil-movement-effective-from-26-July-2026.pdf. Most of it applies to those below compulsory school aged. Where it doesn’t, it explicitly says so as stated on page 6.
Some bits you particularly might find helpful are:
“19. Suspending a pupil for a short period of time, such as half a day, is permissible but the formal suspension process must still be followed. Each disciplinary suspension and permanent exclusion must be confirmed to the parents in writing with notice of the reasons for the suspension or permanent exclusion.”
Also of interest may be:
“20. Any exclusion of a pupil, even for short periods, must be formally recorded. It would also be unlawful to exclude a pupil simply because they have SEN or a disability that the school feels it is unable to meet…An informal or unofficial exclusion, such as sending a pupil home ‘to cool off’, is unlawful when it does not follow the formal school exclusion process and regardless of whether it occurs with the agreement of parents.”
And
“33. A part-time timetable should not be used to manage a pupil’s behaviour”
If your preference for DS is SS but the LA has named MS, did you appeal?
What support is in the EHCP?
When does DS turn 5?
The school nursery should not be saying DD cannot attend unless toilet trained. It also isn’t acceptable for them to call you in to change her. You might find it helpful to read the Supporting pupils with medical conditions at school statutory guidance. It is underpinned by the Children and Families Act 2014 and the Equality Act.
Be careful with SENDIASS. Some are good but too many repeat the LA’s unlawful policies. IPSEA and SOSSEN are better sources of information.