What a humdinger of a thread!....Deafies (and no fault of their own), don't realize how loud they can be!...And hearing children of deaf parents take advantage of it at times and play loud music, wrestle, yell, etc., in the house.....
A "toddler" running around late at night?...Could be the parents are asleep and not knowing this was going on, which is dangerous in itself....
When I lived in an apartment complex, (and I'm deaf), I told my boys (and they are hearing), that we had to respect our neighbors....keep the TV and music on the down low and absolutely no horse-play in the apartment.....they had to go to the park for that....
I also met my neighbors, and told them that any unnecessary noise that bothered them from my apartment, to please let me know! And my boys knew if they disobeyed me regarding "the noise level" and if I got any complaints from the neighbors or the manager, then they were grounded, big time and their computers, TV, video games, etc., would be taken out for 6 months!...And I was very firm on that.
To this day, I've never had a complaint....
In your case, it's different....And I don't feel that you should be the one having to move to a different floor. If you've done all you can do in asking your neighbors to keep the noise level down so you can sleep and rest in peace, then your only recourse is talking to the manager. But hopefully, the deaf mother will understand the situation and remedy it. She just does not realize the noise level that is affecting you.
Good Luck!