when you go to wash the larger container, as long as it has not had anything in it that is possibly detrimental to the snails, the container will simply need a good hot rinse. don't wash it with soap, as any residue will be harmful to the snails. a brand new medium to large size rubbermaid bin that you would find at walmart or some such store would be perfect, and you could use it as a spare quarentine or hospital tank once the babies have grown and moved on.
snails will go to the water line to breathe with their lung organ when the water is crappy for any reason (ammonia, nitrite, or depleted oxygen in the water). my briggs are what keep me on top of my water change schedule, as they tend to hang out near the surface more often the day or so prior to me doing a water change.
those are gorgeous babies, with the spots on them they look like 101 dalmations, lol.
as for food, like msjinkz said, just give them exactly what the adult snails eat, just in smaller quantities and more frequently. you don't need to crush or grind up any food. i feed my adult snails once every two days and my babies once or twice a day.
the babies will fare better in a filtered environment. any way you might put a spare hob or sponge filter on the larger container they will be in? if you go with a hob, make sure to put a sponge or netting on the intake tube to ensure the babies don't go for an impeller ride into the filter.