Blood type home testing kit

[coffeecake]

Hi, I want to find out my children's blood groups but I'm not sure I can use this on them as they are quite young (8 and 5)
It's only a finger prick one and both of them have already had the heal prick as babies (and obviously vaccinations etc...).
Sorry if it sounds a bit thick but I am just after your opinions.
Thanks x

I wouldn't rely on accuracy of that for medical treatment purposes. If it's only a finger prick I can't see it being unsuitable for kids.