Ok, so we've agreed to work on keeping these kids separated - DS will be kept as much as possible in a separate activity group, so that when one group is outside, the other is inside, because it's when they're outside that the normal rough and tumble play becomes a bit sneakier from the older kids. And I can confirm that the two offenders are older kids in kinder.
There are no other available days that suit us and I don't want to switch him when it's only one kid and we have a measure we're going to try.
Thanks everyone