I get ground golden flax meal at costco. I make these pancakes, which my 3 and 5 year olds both love:
http://alldayidreamaboutfood.com/2012/08/walnut-flax-pancakes-low-carb-and-gluten-free.html
I add more liquid than called for in the recipe. And I switch up the add-ins. The recipe calls for walnuts, but I've done berries, pecans, etc. The recipe, without any add-ins, makes great waffles too.
If your purpose to get more fiber into your kid, you might also try chia seeds. I make an overnight chia pudding that is a great breakfast. Here is recipe:
day before eating, stir together:
1 can coconut milk (its about 14 ounces)
1/2 cup milk, cream, almond milk, or whatever you like
1/3 cup whole chia seeds
2 t. cinnamon
1 t. vanilla
1/4 t. salt
sweetener of choice, to taste
Let sit in fridge for 8-48 hours, where it will get all thick and pudding-ish.