Yes and no. You're the mom, you control what your daughter eats and drinks. But I have to say, I think it's a bad idea to give your 4-month-old soda of any kind right now. For one thing, her tummy isn't really set to handle much beyond formula or breastmilk. It's why you're supposed to start babies off on blander, simpler foods: partially to teach them how to eat, but also to get their tummies used to eating things other than formula or breastmilk. You also start slow in order to guage for allergies or intolerances, which in some cases can be quite severe. There's a lot of chemicals and additives in sodas; any one of them can make your 4-month-old very sick, or at least give her a tummyache. If you noticed that her poop was weird after you gave her the soda, or if she was especially gassy or fussy - well, that's because of the soda. The other reason I'd caution against giving your very young daughter soda is because you're setting her up to prefer drinks like that instead of healthier options. Soda is full of sugars, has no health benefits, and destroys not only your teeth but your appetite, too. If she drinks soda, she's not going to want to drink formula/breastmilk, and even though she's getting in her baby teeth, the habits she forms now are going to be with her for life. Any dentist will tell you that kids who have cavities in their baby teeth are much more likely to have dental problems with their adult teeth. Your BF's mom was perhaps tactless in chewing you out for giving your daughter soda, especially in a public forum. But regardless of how she said it, what she said is well-meant, and for what it's worth, I do agree that it's not a good idea to give soda to a 4-month-old.