I would first speak to the mgmt because it is their job to regulate noise - at least give them the option before calling the cops or something. But I would also think about the situation below you - you haven't said what time it was that you were hearing the kids last night, and you do admit that you don't like them, but that's not their fault, nor is it their fault you can't afford to move to an adult-only bldg. If they're only there on wknds, it may be a custody arrangement where the children only get to see their father/mother on those days, and it is also reasonable to expect some noise in an apt. at some time. People do have to live, after all.

Actually she did say the time, it was 9:35. While most tenancies cover no noise after 10 or 11 pm, ANY noise at ANY time of day that disturbs another tenant is grounds for a warning letter and/or eviction if repeated, from the management.
I would definitely speak to the manager about the situation, it would also be a good idea to write down details as they occur such as the date, time, how many kids, how long they carried on etc.
I wouldn't feel bad about speaking up about the volume of noise, lasershow - we all have a right to quiet enjoyment in our rented property. Tenants too often don't want to make a fuss and put up with unbelieveable behavior from their neighbours. If the situation was reversed, half of those noise makers would be the first to complain.

While I agree with Lucy that kids do have to be kids, there's a big difference between a half hour game of running around the house and the same sort of activity or volume of noise that goes on for hours.
Suzan J

I called the property manager this afternoon. The kid noise went on until after 1 AM this morning. Two of them were picked up, but at least one stayed overnight and she was running around until after 1 AM, which meant I could not sleep. And she started again this morning. When I called the manager, and told them this was becoming a regular weekend occurrence, he wanted to know how many kids were there. I said last night at least three, and one of them stays overnight nearly every weekend. He said he would talk to the couple. I had to go out today to get some peace and quiet. Came home after a few hours and it was quiet, then after a while I heard a car outside and it was the woman with the kid being dropped off. They had obviously been out shopping, so that explains the quiet. Now I'm waiting for the inevitable running and jumping to start.

I'm glad you called the property manager. Now it's really important to keep a log of when and for how long and at what volume the noise is occurring - keep a record for the next couple of weeks and if it continues to be a problem, call the property manager again.
If you're diligent about tracking the noise occurrences, your property manager will have no choice but to resolve the issue.
Suzan J

First of all, what are the adults thinking? Geez! One in the morning?
Second, I agree with Suzan J. Continue keeping up on the noise and keep details so you can go to the manager and maybe eventually get them kicked out. They obviously aren't responsible anyways, otherwise those kids would be in bed.

Geez, it was a one time 1am on a weekend, and one time with two extra kids also. Maybe it was the kids birthday, maybe he/she was full of sugar from the birthday cake she shared with only 2 other kids.

lasershow, if you don't like kids you should move to an adults only building.

Be careful about your complaints. You said here that you are paying below market rent. If you complain too much the landlord can just not renew your lease then rent at market value.