What to get after nine assembly toys for young one? (6)

I haven't cracked this one yet — but the brilliant team at Times for the Times have:

I think the idea is that if you’ve already worked on nine, let’s say, Meccano kits, AKA ‘assembly toys’, then the next one will be ‘kit ten’; like all jokes, it loses a bit when you have to explain it. Unless, I suppose, it wasn’t very funny in the first place…