Help?

System: Game Boy Color

I've been trying to remember the name of a gameboy colour game for years! I looked through the whole list of game but couldnt see anything that jogged my memory, so thought this would be a good place to ask for some help!

All i remember is that you have a hammer, and i think that you need to try and find the key for each level to unlock metal gates and stuff. you play as a boy who i think had a red top on and lightish coloured hair, the graphics were pretty simple.
i remember one level where you had to flick switches and i think you were in a fairground kind of place?

any ideas?! its driving me mad!