I want to help my dad and mum with the holiday by paying for myself any ideas but it has to be reasonible times and jobs I will babysit or anything

There aren't a lot of ways to earn money when you are 12, especially because you have to be able to get there and back. So babysitting, yard work, house cleaning, dog sitting and walking are about it, around the neighborhood. If you don't mind unreasonable times, early morning dog walking in the summer is something that a lot of adults with jobs don't mind paying someone to do. Or helping with dishes and small children around dinner time. But you have to be there when you say you will! Put up signs on telephone poles and let parents take the phone calls just in case.
Good luck.