Pump your wheels to the max.
Squirt a whole bottle of WD40 in the bearings...Should do it.
WAIT! Its probably cuz your bearings are unsealed like many bike wheels! Bring them into a bike shop and ask them to re grease them. Btw when you lube unsealed it just doesn't work cuz the lube is too thin, you need to take the axle off and grease them.