Wait til they grow, considering you've already added trochus snails the odds are overwhelmingly in favor of the babies also being trochus. Appearance will be similar at early stages - the common trochus we get is also called the spiral-banded trochus.
Totally harmless, this is free CUC for your tank. The population will stabilize over time depending on how much is there for them to eat. This is why trochus are the staple algae eaters in my tank because they reproduce easily and I don't have to re-stock the CUC.