They are cute ! Same thing happened to me when QT some plants I got found tiny specks crawling around the bowl who each day got bigger. Pond snails so I finally took out most of the plants and just left a small piece in for them till I got some Algae Wafers. I have had them a month now and they are already laying eggs on the side of their bowl which I just wipe out with a paper towel. I use a turkey baster for water changes. They half and inch in size now and yes they are fum to watch.
When I took the plants out of their bowl I QT them again till I was sure there were no more snails and just used my fingers to clean them good while soaking in water I would save from doing water changes. I got lucky cause no snails showed up in my tank with I finally added the plants. They were mostly hiding in the Hornwort the Anacharis looked fine and is growing so nicely !