My DD is just turned 2, and loves a jigsaw. She does 12 pieces.
But, I have observed her, and she seems to actually just be remembering where the pieces go...if that makes sense?
So she isn't trying to find the rest of the flowers, or a red piece that might fit. She scans the table and find the piece she knows goes there.
If it's her first time if the puzzle, she needs a bit more guidance, but can do the 12 pieces. But once she's done it a couple of times, she just remembers.
So, when do kids actually"get" puzzles?
For reference, this is her favourite puzzle atm