Helmet advice for little guy

Looking for good helmet for 2-1/2 yr old grandson. Not ready to put him on a dirt bike for awhile but hes getting on pretty good at the skate park with his scooter and coaster bike and took a block wall to the face a couple weeks ago. I figure he will be riding a two wheeler in about 6 months and trying to copy the big kids at the skatepark. He has a toy store helmet that doesn't fit correct right now.
His mom wants a full face so he doesn't knock his teeth out.
Anyone have suggestions on lightweight full face or good skateboard style helmets that fit little guys. I'm going to measure his head this weekend.