I am no expert, but I read somewhere that 5 minutes of sun exposure on just the face is enough for daily need of vitamin D.
My doctor recommended a supplement, but when I saw it was made by Enfamil I put it back on the shelf and decided it was a ploy and not necessary, lol.
My 3 1/2 yr old was never supplemented, nor was I and we never had issues. I am not a vegetarian though...but sun exposure is what makes the most useful vitamin D.
I say go outside and don't worry about it any more.