OMG there are SO many sponges!!! Where to begin?
I'll start with the most common type of craft sponge that face painters use.
Fantasy World Wide Sponge:
For small faces it's all just sponge control for me, but what you could do is instead of cutting the sponge in half you could make one side a little smaller.
You can find them any place that sells makeup and they are not great for face painting. They are very high density and will only soak up your paint creating lots of waste. Moving on.
Stipple Effect Sponges:
While sea sponge (pictured left) can give a cool stipple effect I find it's a paint vampire (also they never really look clean from the start, which I never liked). They can also leave behind little bits in your paint, are hard to clean and will hold one to bacteria better then any other type of sponge. Remember a 'sea sponge' is a living organism, these are dried out now, but they can be germ factories of not properly cleaned.
IMO they work better for acrylics. They aren't necessary either as a similar effect can be done with practice using a craft sponge.
Or better yet, this is what we use in the makeup industry. This is an orange stipple sponge and can be bought at most makeup FX stores or online. Easier to clean and way more sanitary if you are still looking for that sea sponge like effect.
And this little guy is another FX stipple sponge mainly used for doing stubble, and other things. It's REALLY coarse but lovely if you want to get a scratched effect with your paint too.