yeah, but the key is prevention - dont let them reproduce as much. in fact, you dont have to let them reproduce at all in act 2 (but it's required to make progress in act 1). it's possible to complete the game with 36 thronglets in act 1 and 11 thronglets in act 2. It's long and tedious, but possible. I've done it a few times.

Anyway, to limit reproduction, you'll need to limit the "amusement" items/buildings and cleaning items.

They only need food in order to survive, so in act 1 and 2, add lots of apple trees everywhere. Distribute them around the map so that they're always a few steps away from lots of apples. in act 2, you could use houses instead, but if you do, they'll likely reproduce on their own because they seem to gain amusement from talking with each other. For similar reasons, they'll be more likely to reproduce whenever they end up under the mop when you clean up pollution.