My kids are not foster (we adopted from foster care), but we do use fish oil. They all have brain differences due to drug/alcohol exposure/addiction. Dyspraxia is a 'brain difference' (as is ADD, dyslexia, other learning disorders) and so I would imagine that caring for the brain would help to maximize any therapy you would be doing.
I'd check with the pediatrician and then find a good multi vitamin and fish oil. Nordic Naturals makes a liquid for children that is very palatable. (At least all my little kids would take it! LOL)
You might check into some of Dr. Amen's books.
Change Your Brain, Change Your Life. - Amen Clinics, or Amazon for books by Dr. Daniel Amen, or your local library so you can read them before you buy. The books all concern the brain and how to nurture brain health through exercise, supplements (like fish oil) and 'brain foods' (like blueberries and walnuts).