I am a SN family, so not the answer you are looking for, necessarily, but here goes:
I would be more than happy for you to stay, on the understanding that the children with SN are not 'pushed out' iyswim. The time is one allocated for them to enjoy the facilities, and so they should be allowed a higher proportion of 'goes' imo, given that they may not be able to access the facilities at any other time (and so probably have less chance to overall)
I would be annoyed if NT children/families were dominating the toys/facilities, as generally speaking these SN sessions are such a tiny proportion of the time that parks/whatever are open that it wouldn't be fair if the people with SN were not allowed free reign during the short time allocated to them.