Are You Smarter Than A 5th Grader?

This is a 5th grade math problem. This is not a trick question. It's a real math
problem, so don't say that a bus has no legs and don't include a bus
driver! Read the problem carefully. See how many times it takes you to get it solved.

There are 7 girls in a bus.

Each girl has 7 backpacks.

In each backpack, there are 7 big cats.

For every big cat there are 7 little cats.

Question: How many legs are there in the bus?

I'll post the answer in the comments, but don't cheat! Cheaters! I see you!