I'm not even convinced you're the aunt!
There was no need to do the weighing and measuring you claim was needed for your DC ONLY when this child was in your home. F it WAS a form you would have had it for some time and unless this child lives with you full time you definitely would have had times you could have measured your child when they weren't around - hell even if they DO live with you full time I'm sure there would have been the possibility of a time you could do it without involving them.
There was DEFINITELY no need to calculate their bmi.
No need to talk to mil. IF you were to talk to anyone it should be child's parents but I suspect you didn't do this because you'd have had your arse handed to you.
IF the child is regularly being monitored due to a medical condition the hcps have the knowledge and experience to handle the issue with the child and their parents.
Your attitude to the children's weight is obsessive and unhealthy and imo conducive to contributing to eating disorders you need to adjust your attitude there generally.
"I have an indirect medical background" so you're an occupational therapist and THINK you're an expert on this child's condition and what's needed? That's extremely worrying that someone in your profession THINKS they know better than people better qualified and with more experience. Children's biology, skeletal formation and actions are very different. In addition many joint conditions cause swelling, as can some of the medication used to treat them cause swelling/bloating.
"This child doesn't have arthritis.
He doesn't take any medication." I find it odd that an aunt is so involved in a child they don't have custody of' medical care.
"1 of my DC is a dancer. They like to apply for various programs/shows.Theapplications always require height and weight. I am never very organized and end up leaving it to the last minute." Wow!
1 even more reason not to be obsessive on weight issues, eating disorders rife in the dance world. I also don't think ANY responsible dance company would require a CHILDS bmi calculated.
2 YOU being disorganised is YOUR problem
The more you post the more I wonder if you have an eating disorder yourself. Certainly your thinking around weight is very unhealthy.
The sheer arrogance of your attitude AND actions is SHOCKING!
"(I am fairly sure the forms don't call for that detail)" me too
"I am very interested in that kind of stuff and have done a significant amount of research." The more you post this kind of comment, the more concerned I am that you THINK you are an expert and know better than the ACTUAL experts. To the point I'm concerned this may be bordering on factitious disorder.
At best this is a deeply unhealthy relationship you have with this child that I honestly think you need to distance yourself from.