Neither of mine have been invited to parties of children from childcare (they went two days a week). But we didn't have any parties where we invited kids from childcare either so I didn't think much of it. I think at that age unless they are seeing kids outside childcare on playdates then it's completely normal not to invite them.

But DD1's invites went nuts as soon as she started school - five in the first six weeks! Luckily for my wallet, things have slowed down a lot.