Sorontar, how do you run your client with your kid(s)? My daughter loves playing her single player creative mode with various mods and texture pack....but I do not want this when I play, which gets annoying to constantly change.
How we play probably won't help you...
Sorontar has his own PC he plays on, and I have 2 others, one I play on and MiniObsi plays on the other.... So we have 3 minecraft accounts that get played on 3 separate computers.... So all our mods and texture packs have no effect on anyone else.
I created a local server for us, and the only way I could get it to work was to use https://secure.logmein.com/products/hamachi
to allow the other 2 PCs to connect to the server.
But I don't know how you'd manage 2 accounts on the one PC so that you're not sharing the same gamefiles... but someone here might have experience with that.