Unable to live/sleep peacefully in our new rental

TLDR: 3 bedroom upstairs of fourplex. Downstairs tenant on our side has a 7 year old child with severe anger and aggression, tantrums that have slammed my bedroom window out of the track, flipped over a plant off my shelf from slamming walls, it has gone on until 1:45am on week nights. What can we do? We just signed a one year lease.

Long story long: We just moved last month into a new rental (Upper level of one side of a fourplex) To start, it’s already overpriced for what it’s worth but we were out of options and needed to move at the time. The first 2 nights were fine. However, it’s somewhat been a nightmare since. 4-5 nights (and during the day) per week the 7 year old child that lives downstairs with her single mother is throwing MORE than just tantrums. They will start at about 8pm mainly and sometimes carry into the night until 1:30/2am. I have to be up for work at 6 so this has been detrimental to my sleep to say the least.

We’ve gently talked to the mother and are empathetic to her situation however it’s nearly unbearable. She has given her mom a black eye two nights ago, her mom has permanent bite marks scars on her arms and cuts as her child throws objects, hits, cuts, slams herself into the walls, stomps, you name it.

I took a video the other day because the child’s bedroom is beneath mine and she slammed/ran into the wall and knocked my window out of the track on the bottom. About a week ago one of my plants fell over from the slamming.

Not to mention, she is enraged and screaming/screeching bloody murder until late at night. It has also twice occurred in the early morning on a week day and a Sunday (6/7am)

The mother said this has been going on for 4-5 years. They have lived in this house for nearly a decade.

We gently brought it up to the landlords to which they acted surprised and said they had no idea, they’ve never had any complains and nobody that lives in the other two units beside ours have ever mentioned anything, or the previous tenants before us.

What on earth do we do? We are now in a one year lease and I am barely getting any sleep most days. Even right now in the middle of the day I can’t focus on my house chores because the house is so loud lol