My daughter is 4 years old and is always thirsty and hungry. Any ideas? She weighs 40.8 lbs, also.

Feed her whole meals for breakfast, lunch, and dinner. Maybe even a few fruit snack packets between. Do not feed her unhealthy things such as chips and soda. Obesity in children is on the high, it effects the mind, body, and health. 

Keep her hydrated with a lot of water, as water keeps down the hunger.

Also, make sure she is getting plenty of exercise on a daily baises. Have her go out and rake up the leaves or play in the snow, depends on where you live. 

Only you, her mother, can really know what is best, not the people from here. But I do have suggestions.

Good luck, Katie.