Ideas for Gender reveal/Bday party

[DaisyAnne]

My son is having his 3rd birthday 2 days after we're supposed to find out baby's gender. I thought it would be a fun time to announce if he's having a baby brother or a baby sister to our friends and family then. I'm not advertising his birthday as a gender reveal party, of course, it's going to be his birthday party with that extra surprise.

My original idea was to have him open a box with pink or blue balloons at the very end of his party so as not to make it get in the way of the main celebration (and he loves balloons!), but now we decided to have his party at a bounce house place and we won't really be able to tack it on at the end like that very easily. So I'm trying to figure out some other ideas to keep it a fun surprise, but low-key enough not to overshadow my son's celebration.

I could come wearing a shirt that says something like baby girl or baby boy on my belly so people see it right away? Or my other idea is to wrap up a present for my son to open like a shirt that says "Don't Mess with my Baby Brother/Sister."

Any other ideas? I don't think I'll do the cake thing (I want his bday cake to be separate from this) or balloon confetti thing (too messy).