Around this age, you may start to notice your baby extending her legs and pushing them against whatever is next to her—toys, furniture, the dog 😊—to work her leg muscles.
Try placing your hand and forearm against the bottoms of her feet and see if she pushes her legs against you.
Sometime around 1.5 to 2.5 months, your baby will likely start to kick her legs (while on her back) when she gets excited. You can help her get used to the feeling of kicking by moving her legs alternately while she is on her back, gently and slowly bending her legs at the hip and knee.
If your baby is already kicking, here are some fun kicking play ideas.