Following thread from lilyfire, I thought people might give any suggestions of structured/planned activities which work well when little siblings are awake and wanting attention / to join in.
I find (with 4 yr old and 16 month old)....
Going out for nature walk collecting things.
Building with things like duplo / zoobs which are pretty toddler-safe (but not blocks as he will knock them down as we build!)
Dancing to music of various sorts, playing musical instruments / pans / whatever (as long as you haven't got a headache..)
Short spell of drawing with crayons
Any other ideas anyone?