I had a cheapo savage 22 that I wanted to fit to my 4yo.
I cut down the stock and shaved the grip WAY down. Fit him like a glove, but the barrel was way too long.
I looked up the legal minimum, then chucked up the barreled action in the lathe and cut it down with a hacksaw at 800 rpm. Re-crowned it with a tapered reamer.
It shoots really good and is absolutely adorable!
I didn't care if it shot baseball sized groups at 10 yards, it would work to teach him. Turns out it shoots dimes at 10 yards, so I'm plenty happy with it.