Needing ideas ladies!!!!!

Okay so this is our last baby (so its bitter sweet) We are 19 weeks tomorrow and have hid this pregnancy so far as we wanted to make sure every thing was okay and find out the gender (it's another boy so we will have 2 girls and 2 boys)....any ways my family already knows, but my husbands family does not. His mom and dad are divorced and both remarried. We have a way to tell his dad already. He is a world champion power lifter with world records and we are having a shirt made for our son that will have a saying and picture on it. How ever I am going with his mom and sister trick or treating today with my other 3 kids and I am obviously pregnant. I cannot hide the baby bump any longer. I need a clever way to surprise them.

Side note: I do not have a printer and I do not have a vehicle so going and getting stuff is out of the question.