I honestly don't see a problem with this. Skinny jeans are looser than leggings and I see plenty of little girls wearing those, so unless you have a problem with that, you shouldn't have a problem with skinny jeans.
Honestly, I'm excited that they came out with skinny jeans for little girls. My 6 year old daughter is a STICK. She's a size 6slim around the waist and an 8 for the length. Anyone with tall, thin daughters knows how hard it is to find jeans for these kinds of girls. The skinny jeans will most likely look like regular boot cuts on my daughter, but hey, as long as she can actually find jeans that she doesn't have to pull up every other second, I'm not complaining!