How did you get a toddler ghost??
Two possible ways for sure: either by having a baby with at least one parent who's been revived with the "Oh My Ghost!" opportunity, or who are under the influence of a "Ghost Potion" that you can learn to make with the Generations chemistry set. Story Progression will kill infants and toddlers, and you can easily retrieve their remains from the mausoleum, but I don't know if you can revive them with the opportunity (as I've never tried)...so there may be 3 ways.
Toddlers cannot eat regular meals, so it's a foregone conclusion that Ambrosia is off the table for them. However, they may not be able to be changed into normal Sims at all. You may have to wait until the toddler is a child at least.