Can you put a sealer or epoxy over peel and stick tiles to make them durable and low maintenance

Unlikely... because most peal and stick tiles are flexible by nature... and any coating you put over them will not be as just one thing... also some peal and stick tiles have the same color throughout (but not all do) and the "coating" will be less durable than the material under it.

Question: And an important one. What will this be used for? Proper selection of the tile for the expected usage is critical.

You can apply a liquid wax but it will not be tougher than the surface you have now. Regular and repeated waxing may extend the life of the tile but they frequently last for 20 years on their own. What is the issue you are dealing with?

I have novalis planks on a daycare floor, they are just over a year old and are starting to show quite a bit of wear.I don't think they will last long

Not sure which model you have but they should have a limited lifetime warranty NOVALIS (http://www.novalis-intl.com/fashion.html) I'd call the local distributor about your issue. They may not stand behnd the product if your planks are residential as opposed to commercial, I don't see that they sell commercial flooring. This is from their maintenance manual "Apply 3 coats of high quality acrylic floor finish according to label instructions. Be sure
to allow the proper drying time between coats."