Regarding toys for 4-year-olds, I think the caller might be stressing about it a bit too much. Like Paul said, kids that age really aren’t too savvy about what they want. To them, everything is new and you can never really tell what’s going to resonate or not. Even with my own kids, I’ve bought my kids stuff that I thought they would love only for them to be apathetic about it. Which, I agree with Paul, is almost worse than getting them nothing. I have also seen them fall in love with stuff that I never would have guessed. For example, I did a charity run a couple weeks ago and they gave us participation gifts (or whatever you call it) that included a cheap, plush Chik-fil-a cow. My youngest son sleeps with it every night
I would suggest either doing what Paul suggests and ask the parents (even though that’s not even 100%) or just find something that looks cool to you. I would avoid licensed stuff unless you know for a fact the kid is into that specific character. Your best bet is to go with something arts and crafty. Something they can actually do something with.
However, whatever you do, don’t get things that make noise. I have an almost identical story to Paul’s regarding a toy train. These things get so loud it actually hurts your ears when you turn them off. And when you finally get fed up and take the toy away because it’s “broken,” you have to deal with disappointed children - which is never fun.