Why is oil coming out of my Kid's bike

I took my kid riding on his KLX 110 over the weekend. I noticed that whenever he dumped it on its left side (I think it was only when he fell to the left), oil came out of the engine. The oil that came out was more than a few drips, but less than a steady stream (if the bike was on its side long enough, there would be a small puddle of oil).

Is there any sort of vent hole/hose or other thing that allows the oil to come out in this situation? If not, what else could it be?

Thanks in advance for any advice.