Rollerskate is signed a lot like skate. The number of fingers you use to sign would depend on whether you are referring to roller skating or ice skating.
To sign rollerskate, curve both the index and middle fingers of each hand, hold them facing up, then make side-to-side arcs as in a skating motion, suggesting the two sets of skating wheels per foot.
Teach your toddler the sign for rollerskate when introducing them to basic skating skills.
Skating is an advanced motor skill more suitable for toddlers. Teach your little ones the sign for rollerskate when they see their older siblings skating, or when you first introduce them to the basics of skating.