So my 6 yr old hit her chest earlier got a bruise and now I'm afraid?

In cases like this it is always best to go and see a GP I am sure you agree it's sensible as they have the backup to deal with all the little nicks and knacks that come up in everyday living and we should make use of it. I can tell your foresight is cautioning you to look into this matter as you mention all sorts of things can result.