Milk replacement in baking recipes

Another option is to avoid a milk substitute. When I dealt with a similar situation, the wide variety of non-dairy options did not yet exist. I often used water in place of milk with good results.

Thank you all for your thoughtful and very helpful answers. I have lots of options to try with the little guy this weekend :)

In addition to almond milk/soy milk etc look into cashew cream. It's easy to make with raw cashews, water, and a food processor. Chef Tal Ronnen has a celery root soup recipe that calls for the cashew cream that is TO DIE FOR. I have also used it to make my own versions of creamy of mushroom soup. Easy and versatile, she'll thank you for it!

For any recipe that requires buttermilk, you can sub soymilk or coconut milk with 1 tsp apple cider vinegar per 1/2 cup of either of these. It'll add enough acid to your recipe to still create the lift from the buttermilk and baking soda reaction. For example, see my recipe for Black Tea Pumpkin Bread. I skip the milk substitute completely and just use black tea and cider vinegar. It works just the same as if I used 1/2 cup buttermilk in the same recipe:
http://beyondcelery.blogspot.com/2012/03/black-tea-pumpkin-bread.html

Yes, you can generally use soy, almond, rice or coconut milk interchangeably with cow's milk in cooking. There are a few things to keep in mind -- each of these tends to have their own flavor, with rice milk the most "neutral" and least offensive to my taste buds. As both soy and nuts (peanuts and tree nuts) are considered on the "top 10" food allergies, rice and/or coconut can be the "safer" choices if you have any concerns about other allergies (also, a very high percentage -- over 90%? -- of the US soy crop is genetically engineered. If that is a concern for you, then make sure you buy organic so that you know the soy isn't GE). Personally, when the recipe is one where a little fat makes a difference (okay, that's 99% of all recipes!) coconut is the best choice flavor-wise.

A few other thoughts. My youngest was lactose intolerant as a young child (she's 14 now and grew out of it before age 10) and we discovered that it was really cow's milk that was a problem, so that enabled goat cheeses. She was also able to tolerate yogurt (the enzymes in yogurt make it tolerable for many -- but not all -- who are lactose intolerant). We also found that if she had a Lactaid pill (an enzyme) BEFORE eating something with cow's milk (like pizza or mac and cheese or ice cream) she didn't have any resulting tummy trouble.

Good luck! It is amazing how many of the foods we consider "children's foods" have cheese or cream in them, so it is a challenge.

You can sub soy milk or rice milk in cake recipes. You can also use soy margarine. With margarine check that there are no milk solids. Willow run and Earth Balance are good. Will your child tolerate Lactaid milk?

Depending on the recipe, I know that a lot of vegan bakers do make that substitution, as well as lots of others. Again, always depends on the recipe you're making. Since your child is lactose intolerant, I would read about vegan baking! There is a LOT of great info on line about it. Here's a few places to start :
http://www.peta.org/living/vegetarian-living/baking-cheat-sheet.aspx
http://www.theppk.com/vegan-baking-the-post-punk-kitchen-shows-you-how/