This is driving me bonkers but the kids have their own bathroom and the seat in there is constantly under stress, either being sat on the wrong way round, climbed on or slammed shut.
I've just found it totally off its lickle plastic hinges and screamed at ds1 largely because he is Tha Sort Of Boy and two days ago he sat on the curtains in there, cue 10ft high curtain rail coming down plus half the wall. He breaks everything 
I need a decent, very strong loo seat so please, if anyone else has encountered a wavering seat would you be kind enough to let me know if you have now found a good one that stays still! 