So an occasional birthday cake so all the kids have a bit of fun is OK with me.

There can be two or more  b'days a week  in a class, at least one, when you have 20-30 kids in a class/centre... not just occasional.

That is one reason some pre-schools, schools have banned children bringing party food from home altogether,  now the focus is on healthier food with less fat & sugar. The children could be getting 2 party cakes or more  in a week.