Should I apply for a grocery store job?

I am 13 years old and really want a part time job doing carts or anything at no frills. My brother works there and he says there is a 13 year old kid(maybe 14, not too sure) who works there so I know the hire young kids. I want to apply to a store like that, are there any other stores that hire 13 year olds and i should apply to as well. SHould I go into the store and ask to speak to te manager or what should I do once I walk into the store. Please help :)