First off I have to give credit where credit is due. I saw this idea on Thrive, she has a tutorial on how to make woman's knee socks into tights for girls (if your child is older, hop on over to her tutorial for a larger version than the one I'm making here) oddly enough we used the exact same socks, total coincidence. Since my child is a bit younger I had to modify my version a bit so I will share a tutorial with you for the toddler size. Thanks for the inspiration Thrive!
Pair or woman's knee high socks, mine were like two bucks at Target
Old leggings or tights (or child size boxer briefs)
First you will need to turn your socks inside out and put them on your child's foot. Line the child's heel up in the heel of the sock and mark where the toe ends. With that mark as your guide, cut the toe of the sock off mimicking the round curve of the original toe. Sew the new toe shut.
Turn your socks right side out and your your leggings inside out. Insert a sock into each leg hole (right sides together) making sure to point the toes of the socks to the front of the leggings. Pin and sew around with a zig zag stitch.
I was completely surprised that the feet of the socks weren't way to wide for my two year old, but the heal fits perfectly and they turned out adorable! The length of the legs and the stretch of sock material even gives her some room to grow!