MOT- i wasn't going to post, because it's not my thread, but the information you were given seems odd.....
Yes some kids don't have an issue with lactose, it's the protein in dairy that causes issues. I initially though we had a lactose problem, but after some anti-body testing we discovered it was the protein causing problems.

If you have an issue with the protein, then lactose free certainly doesn't help, you need something without the dairy protein. Soy, Rice, Oat, Almond, any milk from a plant wont have that protein. Goats milk has trace amounts of the protein and is suitable for some people but not others, obviously depending on the severity of the intolerance or allergy.

I am not having a go at your decision to give your kids soy, if it works for you and you're happy with it, then that is great.