That's a good question. I would definitely tip them for the baby -- the question is whether you tip the same amount as an adult or 1/2 the amount. I guess I'd tip 100% for the waiter since I know that when my son was a baby and cruised, he'd make more mess than adults for the waiter to clean up! ALso, you may have to ask for spec'l requests for the toddler such as pureed vegies, etc.
You could also ask the guest relations desk on your ship for guidelines too.
Luisa Frey Gaynor
Family Cruise Editor