Also while I was infuriated at Colin's parents for not taking Andy's warnings seriously, i'm not so sure that would've prevented Colin's seizure as Dr Brown made it clear that the bone fragments were so small they wouldn't show up on scans until a serious incident happened. So even if Colin was under observation 24/7 he probably still would've had the seizure because there was no way of detecting that fragment in his bloodstream before it got to that size.