VERY loud child upstairs, what to do?

I moved into a new apartment 2 months ago, and it’s been great and lovely. But, there is a family upstairs that has a child that stomps and jumps for a long period of time at all hours of the day. It is INCREDIBLY loud and disregulating, it shakes our apartment. I didn’t want to immediately approach them about it, but one night a few weeks ago the kid was jumping past 10pm so I started pounding my broom on the ceiling. I can hear the parents walk back and forth, a chair move, and even the kid running across the apartment. That is not a problem with me, this game the child plays is something of an entirely different nature.

I wrote them a very friendly card a few weeks ago, telling them that I want their child to be able to play freely, but I also want peaceful enjoyment of my home. I offered to give them some play mats to put down where the kid plays and gave them my phone number. Mind you, our lease does have a clause requiring all floors must be covered with rugs or carpeting, as well as a clause telling parents to be cognizant of noise made by children. That night I heard some more jumping, then after that it stopped. I thought, oh great they got the message.

Wrong, it felt eerily quiet. Last night I heard adults walking upstairs and some suitcases rolling and then BAM, the kid starts jumping and stomping. The must’ve been on a long vacation. I’m at a breaking point, my anger and frustration is causing conflict with my partner, and I have to wear earplugs at all times to just be able to not freak out.

Should I knock on their door? Or just go straight to management? I want to give them the benefit of the doubt, but am afraid they’ll just be combative and react. Please someone tell me a success story you had, we spent so much money on this move and love this place after the struggle and stress of apartment searching but this kid is breaking me.