Considering she is now with you a lot of her waking hours and eating healthy portion controlled amounts of food and getting exercise over time it should help her to at least not gain any more and more probably actually slim down some. Toddlers often look very overweight if their height/weight/size isn't in sync yet. The toddler belly disappears for most kids when they learn to run and climb and be more physical. I see nothing wrong with sweets. Portion control would be the biggest thing in the sense of I give you up to a canada food guide serving of a food and have to be convinced for any more than that and never of the starch part of the meal. If you are still hungry I'm sure I can find a fruit or veggie for you to eat. I wouldn't bring it up with the parents at this point and especially since any weight discussion is going to be seen as you making accusations about them not just their child. How much experience the child has had to be able to move will be a factor too in the sense if the parents aren't inclined to go for a walk after dinner the child isn't either. If in 6 months she is no better or gets worse then I would for sure bring it up with the idea of you want the parents to speak with the doctor so you can get a nutrition assessment to know how much and what to serve - what you really want is the parents to get that info.