The definition I’ve heard the most is: newborn (0-3 mo.), infant (3-12ish mo, toddler (from the time they start walking to between about 2-3 years). Technically, any of them could be considered a baby.
“Toddler” describes the action of toddling, or walking in an uncoordinated way.
I used to make fun of vegans too, now I am one. Othering a group of people might seem like fun, but just make sure you try not to think too hard about their position. I think you’ll be ok though.