Vitamin supplements and breakfast cereal - is this an overdose?

[Countuptoten]

When my DS is a bit under the weather I usually start up with a centrum children's vitamin tablet for a week or so as he is a bit more picky about eating. I suddenly thought this morning whether if he eats a Weetabix too if that means he would be overdosing on some of the vitamins as Weetabix are fortified. I know the vitamin tablet contains 100% RDA of folic acid and biotin and Weetabix has folic acid has folic acid too?

Don't worry anything we don't need just gets excreted and since our bodies prefer extracting vitamins from a natural source (whole foods) rather than synthetic form he probably just excretes it all anyway.
There was an interesting programme on recently where they measured how much the body uses after taking large doses of vit C the results showed that the volunteer doctor/presenter actually excreted more vit c than he took.
The only vitamin we need in this country if we eat a reasonably healthy diet is Vitamin D during the Winter months due to lack of sunshine.

I have to take folic acid as I can't store it. If you require it at drug levels you take nearly ten times what a pregnant woman takes. It is enormously safe.