Have you ever wondered why babies scratch themselves so much? It's because they can't really control what their arms and legs do until they're about six weeks old (intentional movement comes much later, at around four to six months).
Newborns' nails are soft enough that they don’t require frequent cutting – they are usually worn down by the baby's clothing. As your baby becomes old enough to interact with her environment, her daily activities will also help wear down her nails.
Your baby's nails grow quite fast. You can cut or file (using an emery board) fingernails and toenails as needed – rounding off the nails so they are smooth.
Try to do it when your newborn is asleep, very calm or drowsy. For older children, you can use a high chair or car seat where the child can be strapped in.