When it comes to babies, milk really does do a body good. But the best type of milk for your baby will vary depending on his age — and, until he’s a toddler, will likely change from year to year.

Until your little one is 6 months old and starts solids, breast milk or formula will be his sole source of nutrition, supplying all the fat, protein and carbohydrates he needs to grow.

After his first birthday, he’ll get much of his protein, calcium and vitamin D intake from whole-fat cow’s milk, then may make yet another switch to reduced-fat milk by the age of 2 (though doctors no longer recommend it and say children can continue drinking whole milk).

Overwhelmed? Don’t be. Here's a guide to the best types of milk for babies of every age. 

Under 6 months

For the first six months, babies get all the nutrition they need from breast milk or formula. Breast milk, in particular, is packed with just the right amount of protein, sugar and fat that your baby needs to grow (in an easily digestible form), plus antibodies that can help boost his immune system and help fight off illnesses.

In fact, the American Academy of Pediatrics (AAP) recommends breastfeeding as the sole source of nutrition for babies up until they're around 6 months old. After that, mother and baby can continue nursing for as long they want.

Formula also provides plenty of nutrition for your baby, and manufacturers try to replicate breast milk as much as possible. Along with protein, sugar and fat, some formulas are also fortified with probiotics, iron and vitamin D.

Whether you decide to breastfeed or bottle-feed, rest assured that you’re giving your baby all the nutrients he needs to develop and thrive. What isn’t a good idea, however, is giving your baby cow’s milk if he's under the age of 1.

Not only does cow’s milk contain higher amounts of protein and minerals — which can be hard on little ones’ sensitive digestive systems — but it also doesn’t contain the proper amounts of vitamins and minerals for babies who are younger than 12 months.

You should also avoid giving your baby alternative milks such as almond milk, soy milk (except for soy-based formula), rice milk, cashew milk or oat milk because the amount of nutrients can vary.

6 months to 1 year

Somewhere near the 6-month mark, your pediatrician will likely recommend that you start introducing solid foods to your baby, including dairy products like whole-fat cheese and Greek yogurt. Once he starts eating solids, you can also offer him sips of water from a sippy cup, straw or open cup with his meals.

However, you shouldn’t add cow’s milk (or any other alternative milk) to your baby’s menu just yet. Until he turns 1, the only type of milk he should drink is breast milk or formula because his digestive system is still sensitive, and he needs all the nutrients (like vitamin E and zinc) he can get.

1 to 2 years

If your baby is a year old, he’s likely ready to kick the bottle and switch from formula to cow’s milk. Cow’s milk contains fat, protein, calcium and vitamin D — important nutrients that your little one needs to grow.

Most 1- and 2-year-olds should drink about 2 to 3 cups of whole milk each day, according to the AAP. (If your baby has a family history of heart disease or obesity, or is at risk for either one, you can ask your pediatrician whether you should offer him reduced-fat milk instead.)

Not all babies take to it right away, however. If your little one is struggling to make the switch, try offering him a blend of cow’s milk and formula or breast milk to help him get used to the taste. You can also try adding a splash of cow’s milk to his favorite solid foods, including oatmeal, smoothies or even mac and cheese.

If your baby turns up his nose at cow’s milk altogether, don’t panic. Babies can still meet their dairy requirements by eating whole-fat cheese and yogurt.

It’s not a good idea, however, to entice him with flavored milks. The AAP says that children under the age of 2 should avoid all added sugars — including those found in chocolate, strawberry and other flavored milks. Plus, introducing flavored milk at a young age may just make it harder to transition to the plain stuff.

Try, too, to steer clear of plant-based milks, such as almond milk, oat milk and cashew milk, which usually don’t contain as many nutrients — including protein and fat — as cow’s milk.

Goat’s milk also isn’t recommended for babies, according to the U.S. Department of Agriculture (USDA). Not only does it lack important vitamins and minerals, including iron, folate and vitamins C and D, but it can also be hard on a baby’s kidneys.

One exception to the alternative-milk-rule is fortified soy milk, which can be given to tots who have rare medical problems such as dairy allergies or lactose intolerance, or those whose families don’t eat animal products.

Soy milk is the one alternative milk that’s nutritionally equivalent to cow’s milk, and is therefore considered an acceptable substitute. 

2 years and up

Toddlers who are ages 2 and up can make the switch from whole- to reduced-fat cow’s milk, i.e. nonfat (skim) or low-fat (1 percent) milk. At this age, most children will need to drink about 2 to 2½ cups per day, according to the AAP.

Why trim the fat? Switching to a lower-fat milk can cut calories from your little one’s diet, which helps him maintain a healthy weight. For this reason, it’s also a good idea to avoid (or at least limit) flavored milks like chocolate and strawberry milk, which contain added sugars.

You should also think twice before serving up “toddler milk” (also known as “transitional milk” or “weaning formulas”). These milks tend to be marketed as “big-kid formulas,” but many of them just consist of powdered milk, vegetable oil and corn syrup or other sugary sweeteners, which just add more empty calories to your child’s diet.

Even alternative milks — including almond and cashew milk — aren’t always healthy substitutes for cow’s milk in children under the age of 5.

Most alternative milks don’t contain as many nutrients as the cow’s kind, and some experts think that people may not absorb nutrients from plant milks as well as they can from dairy milk.

The exception to this rule is soy milk, which is nutritionally equivalent to cow’s milk. Tots who have dairy allergies or lactose intolerance, or whose families don’t consume animal products may be able to stick with soy milk. Just consult your pediatrician first.