Scooter wheels spinning poorly?

My son's scooter wheels are spinning very poorly. What would cause that? Rust, grit, or something else? It's only about 2 months old and I can't imagine it rusting that quick on the inside (though it's winter here in Australia at the moment); and I think he's generally kept it out of the dirt. And what if anything can be done to fix it? Take the wheel apart? A particular lubricant? It's a pretty good scooter (Madd Gear pro) with those standard small scooter wheels.