Dog becoming aggressive, especially when baby is around?

Maybe he's not feeling well? My 100lb yellow lab gets like that when he's sick or tired of our other dog trying to play. My lab is now 7years old and just not that energetic and like to sleep more. But if the younger dog comes up to him he growls and snarls. He has never done that with me yet though. We also noticed that his eyesight may be failing. Maybe call your vet and express your concerns. Maybe they can tell if his change in behavior is medical. Either way they should be able to help you with what needs to be done to stop his behavior.