J.M.
Formula is basically exactly the same, except for those with added DHA and such. I did the same thing with my daughter, started her on the similac because I had those sample cans at my house but switched the enfamil because I personally chose it based on the DHA values. I did talk to her peditrician about it, and she said it was fine. Some babies may have stomach sensitivies, but my daughter had no problem switching at all. Congrats on being a nana! I have a nana too, haha