I would ( and did) tip full amount to waiter for your toddler. She sits in a high chair and eats and as noted above I am sure she leaves a mess.( all little kids do!)
As for the cabin steward I do think we left a little less then full amount, but more then half, this was years ago so I am not quite sure, I do remember that the baby slept in our bed and I kept the cabin clean so I don't recall the steward having to do that much more for the baby.
Does the cruise line your're going on have written guidelines for this, some do charge 1/2 for small kids, some still ask for full amount.