Ds (5) was not the only boy at the Tea Party! He went twice (once when he was four and again when he turned 5). He loves the Mad Hatter so even though DH wasn't crazy about it the first time I signed him up with his sisters. I think there were about 12-15 kids there are there were about 3 or 4 boys. I think more and more boys are starting to do this.
My kids do this every year, in fact I already have an ADR for all three of them for July. (BTW - DH finally got used to it.)