What to do at a pizza party for 12 - 13 year olds?!

For the most part, the guest will entertain themselves with chitchat and such, but back up games are a good thing to have in case the party starts to become dull. Have silly games like pin the tail on the donkey and musical chairs. You can also have board games ready to play. Music in the back round adds a fun effect.

are they girls or boys (or both)?

if they're girls they will probably just entertain themselves by talking the whole time.

and boys probably won't want to sit at a table for an entire party...

i work with 13 year old triplets

Musical chairs , truth or dare, would you rather ,

Make out.

lol dont do bingo XP
ask them what they wanna do :)

have water blow ups