Why would anyone want to let there child sleep on the floor? You can't have a purse/back pack on the floor (for takeoff) but a child is ok. I was on an Alaska flight a couple of years ago (in 1st) where the mother had a new born (very new) in her arms and a 2 year old spent the whole time on the floor. They had to fly first class but couldn't get seats for their children. Even if you child has a seat, keep them buckled up. Take off or not I don't think anyone especially children should be on the floor. Let's use some common sense.