Mixing languages

There are 2 things I am nervous about when I think about the future:

 - my child will start speaking really late because 4 languages might be too much for her

- she will mix the languages and no one will understand her. Although a plus (or maybe a minus?!) of our environment is that each language comes from a different language family so the vocabulary and grammar is totally different.

Here are some articles about raising bilingual kids:
http://ezinearticles.com/?expert=Christina_Bosemark