S.B.
I so love Halloween.
I would ask the 11 and 8 year old what their ideas are and go from there. The baby is pretty much along for the ride and won't care.
Pirates are super cute and easy costumes.
What about the 3 Musketeers?
The best costume my son ever had was a pirate. You would faint if you knew how simple it was.
Have fun!