Fun ways to tell my kids #3 is on the way?

They’re gone for the summer to stay with their dad like usual so I won’t get them back until August 4. I’ll be about 12-13 weeks then. I want to have a surprise waiting for them when they get back or shortly after. Their dad’s new baby was just born a few days ago and they’re IN LOVE with it so I know they’ll be over the moon! PLUS this baby is due on my daughter’s bday so it’s extra special! They’re 10 and 6!