It's hard to find little projects that are suitable for toddlers. The attention span, the fine motor skills, the fact that you don't really want to fill your house with crap. This one, from Prudent Baby, was perfection.
They got to dump, to stir, to dump again, to stir again, to spoon... And then it got to leave the house and be genuinely useful. BAM!
Mix the gelatin with water.
Add bird seed
Spoon into cookie cutters.
If you're a toddler: Assume that the moment after hanging, all neighborhood birds will dive bomb your feeder immediately. Feel confused when this doesn't transpire.
If you're an adult: Pretend that something other than squirrels are going to enjoy the bird feeders.