A good way to start the day would be oat (I add vanilla and cinnamon for some flavour) add a teaspoon of ground flax seed or a teaspoon of chia seeds
to your oats, both will provide you with
omega 3.
A little bit of knowledge can go a long way and all this info is readily available and I found it all very useful when switching to a vegan diet.
It would be a shame for someone so young to suffer permanent damage from being underweight.