Any dairy kefir grains will be fine. It takes a little time for grains that have been in cow dairy to acclimate into goats dairy, say 2 batches(because your amount of grains will be small at first your first few batches will be small as well, also you can totally still cook with batches of milk that did not fully culture)... but after that they should culture to infinity and beyond with proper care.
Note: Pasteurized goats milk is fine to culture, but NEVER ever use any "ultra pasturized" milk products.
Milk Kefir Grains | Dairy Kefir Starter Culture
This link has grains and some info on culturing.
Things to do with good whole milk kefir to make it irresistible... add about a 1/2 tsp of vanilla bean paste and a drop or two of stevia to a cup of it. NOM!!! dessert "shake"!
Stick blender an apricot into it!
Make a water-butterfly... 1/3 milk kefir, 2/3 fruit water kefir(also full of good bugs). Like a probiotic italian cream soda!
You're boys will love their bacteria in no time I think!