Did you have any problems doing these before you had your baby? Does your inner thighs feel stretched when doing these or strained? If your straining your inner thighs, it sounds like your outer thighs need to get stronger. Are you jumpin up before you spread your legs or landing before you can get your legs back under you? Maybe, you're using your inner thigh muscles to bring your legs back together before you land? If it's a stretching sort of pain, maybe you just need to stretch it a little more during your warm-up.
Until you get stronger, jumping up and down is a great way to keep your heart rate up. You could also sub frog leaps side to side or front to back.