A few weeks ago I was fretting over what to get S for her birthday. My house looks like a toddler bomb has hit it; she has every type of toy she could ever want, and I didn't want to waste money buying more junk to pile in the corner.
Then I went to a Stay & Play session at nursery, and saw her playing with something... her keyworker came over, and told me, "Ah, S loves this. She plays with it til the batteries run out, and then she comes to find one of us to ask for more!"
The toy she was playing with was this: