Oh gosh, I’m sorry that happened to your son!
Children’s doses are all weight based, whereas most adult drugs are generic doses. So everything has to be calculated properly and then checked for accuracy. There are some trusts that allow single checking for certain drugs, or some trusts that have the Nurse in Charge do all the control drugs (use of experience etc), or sometimes checking is done in the medication room against the drug chart and then distributed from the trolley by the Nurse with the trust it won’t be tampered with. Sadly everywhere is different, but I’ve always been taught peadiatric drugs should be double checked.
Sadly anything could have happened. Too much morphine, your son reacting differently to the correct dose than expected, doses too close together, or yes just human factors - I’m not afraid to say I’ve made drug errors (nothing life threatening) when tired or busy or in an emergency, even with a second Nurse checking. Whatever happened, I imagine teaching and changes came from your sons situation, whatever the cause was. I know that doesn’t help but definitely my experience of such scenarios. X
I also think meddling with drugs would be difficult due to frequent drug stock checks, drugs being locked away, cameras (sadly not in every trust), computerised systems, staff always being around. Lots of reasons. But I guess if you really want to do something awful, you’d find a way sadly.