I completely agree with Greg about "gonna." It looks wrong every time I see it on these forums. For the most part, native writers do not write the word "gonna." Most of the time, we do not say "gonna," we say "going to." We say it really fast and we slur the words together and it might sound like "gonna," but if you asked someone to write down what they said - they would most likely write "going to."
Just remove "gonna" from your vocabulary. It does not make you sound more like a native speaker. Definitely do not write it.
"I'm going to give you a bath."
You could also say "I'm going to bathe you." But "bathe" has a slightly formal tone and it isn't what I would say to a baby.
"I'm going to breed you" just sounds disgusting. I am not sure what you mean, but it almost certainly isn't that.
(If I wanted my dog to have puppies, I might say "I want to breed her with the neighbors dog, so they can have puppies.")