How to stop annoying the downstairs neighbors?

Our neighbors stopped us in the hall and asked us to be more considerate. They asked if we had kids because it's not about me or my husband though, it's because of our son. These places are cheaply made (apartments) so the floor is flimsy, warped, wood lenolium. He just turned one and is still crawling so they can hear him. Hand, knee, hand, knee, fall, drag the remotes off the coffee table, stuff like that. My husband told them but they didn't seem amused, just told us to keep it down because they can hear constant thumping and she works nights.