Assassin Snails Eggs

I think you won't know you have babies until they grow a bit bigger as they hide in the substrate. They will find food for themselves; if you are worried grind some food to powder as they will eat commercial food without other snails to eat.

As for cleaning the tank, you could use my method with the tank that has cherry shrimps. Go through the old water with a jug, checking each jugful carefully for signs of life. It takes twice as long to clean that tank as it should 

Here you are - everything you need to know about assassin snails. And Sulawesi elephant snails as well 

Thankee Sue just what I needed and yes I do feel a bit like an expectant mum