Give her 1% milk instead of 2%, or 2% instead of whole milk, that will reduce the fats she in in taking by double the milk she is getting. Or, offer her rice, almond or soy milk too. Milk is a much healthier alternative than cereal. I haven't ever heard of 3 cups of milk as a limit for a toddler.
Also, she may like the cool taste of milk, so offer her cheese sticks or yogurt.
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Okay, the constipation thing makes since now. I also remember that a lot of milk consumption can give them full tummies so they won't want to eat at meal times, so offer the milk as a snack after meals.
Soy milk is good for constipation because is soften's stools so that could be a great compromise. Also more fiber,:
"Increase the amount of water and fruit juices (minimum of 2-3 glasses) that your child drinks each day.
Increase fiber: Increase the amounts of fruits and vegetables that your child eats. Raw, unpeeled fruits and vegetables (especially beans, sweet potatoes, peas, turnip greens, raw tomatoes and corn) have the most fiber. Popcorn also has lots of fiber in it. Give enough grams of fiber to equal their age in years plus 5 each day (check the nutritional label for high fiber foods and snacks with at least 3-4g of fiber per serving). Vegetable soups are especially high in fiber and also add more fluid to your child's diet.
Increase bran in your child's diet by offering bran cereals, bran muffins, shredded wheat, graham crackers, or whole wheat bread."
http://www.keepkidshealthy.com/toddler/toddlerproblems/co...