Is flavored milk so bad for my 16 month old?

This is our third time trying to get him off the bottle. I finally threw the bottles away this time, so I am not tempted to give him one in desperation. He will kind of drink it from his new cups with straws. Which is a HUGE thing, since this is the first time ever he has come back for repeat sips. But, the problem is, I can only get him to drink a couple ounces a day. I was wondering about adding chocolate or strawberry flavoring, but I wanted some opinions on this before I got started. Thanks so much!