You can use your credits for any meal you want on any day. If you wanted to, you could use them all on the first day.
So if you want to have a breakfast buffet and a dinner buffet on the same day you can do that, as long as you have enough credits in your account to cover them.
And if you want to have a TS breakfast and a CS dinner you can do that, too. Or if you want a sit-down lunch and a buffet dinner.
I am not sure what the question has to do with having a baby. A child under age 3 would not have any dining credits, but would eat for free at buffets.