When making soft-sole shoes for toddlers and older children you may want to consider some sort of waterproofing

for the soles.

The easiest way of doing this is to make the outer sole area from Toughtek.

PUL is a polyester knit fabric with a waterproof laminate backing.
By sandwiching a sole cut of PUL between your lining and sole of your shoe you can provide a level of waterproofing

You can also coat the bottom sole in a liquid plastic called Plasti-Dip.

You can buy Plasti-Dip at most hardware stores in the paint section.