I have my own 11 month old and watch a 9 month old all week and playing with 2 babies and a 4 year old all day can get tedious, but it helps to introduce new games and ways to play.
We played with tupperware, measuring cups, puppets, play dough, and pom pom balls!
Hiding things in the tupperware and having him find them was a hit, as was him putting his face in the containers!
He loved exploring the play dough (and since it was homemade, I figured it was ok for him to taste it too!). He also tried tasting the pom pom balls, but wasn't very thrilled with the taste of those.
We also found a shaker that my older son and I made when he was younger and the babies liked exploring with that as well.
It's also never too early for learning their alphabet!
We also made Baby Egg Carton Balls and everybody loved these. The babies and my 4 year old could throw them without fear of getting hurt. They had a blast!