I know when I first saw these I laughed my a$$ off. Then being pregnant and being a yoga instructor people have mentioned them to me very often and I have checked them out at baby stores. They come in some great colors and are super soft and cute. There are many companies out there, but I give Small Plum the credit for doing them the best with simplicity, colors, and making them out of bamboo.
I do have a pattern to upcycle them out of an old adult shirt and my baby will have a bunch of upcycled ones, but perhaps a pair of two of dress up bamboo yoga pants too. Here is a link to Make Baby Stuff and their baby yoga pants tutorial.