Can we get out of lease due to LL not helping solve a problem?

It sounds like your neighbors are annoying, but not breaking any laws. In which case, there is not much that the landlord can do. Kids make noise. Is it excessive? I'd have to be there and see it to decide. So you don't really have a good case for breaking your lease. How much longer do you have to go? It may be best to just tough it out if it's not too much longer.