Why do toddlers like rain puddles?

Puddles are an extension of water play. Have a look at the learning aspects of water play for a really well rounded answer. Psychologically most adults prefer that kids don't play in puddles so it is also a test of boundaries.

As for designing good rainproof gear- knee high rain boots would be better than calf high and I think that raincoats should have detachable hoods that also have an elastic along the forehead to keep them from falling off.

Rain Puddles are cool, to see how high the water splashes. It's also an exciting experience for a toddler to learn that he can control his world by his actions. Kids this age learn best by doing, so if they do something (like jump in a puddle) and they see the consequence of their action (like the water splashing, or Mom's jeans getting all wet), this is the first time they learn the concept of "if A, then B"

they think it is funny entertainment I guess or at least that is what my daughter seems like her reason for jumping in a puddle in the rain

because...its is something that mothers don't want them to do. Unless it is for fun. I always say when it is raining before we get out of the car..to go to a store. DON"T JUMP in the puddles!

Its something you say not to do...and isn't a big deal! No real punnishment. so they do it!

who doesnt like jumping in rain puddles?

ask a few toddlers. who can tell you better then they can?