Garden Snail

I was walking back home in a summer evening when I spotted lots of snails on the garden wall. There were a few big ones, and a lot of tiny ones. I hope the bricks can give an estimation of their size. I don’t know whether the tiny ones were babies hatched, or another kind of snails hanging around the big ones. The tiny ones looked different from each other, maybe different species or just not so look alike siblings! Anyone has got any idea?