Am I right to cross out "gender" on my child's school form and change it to "sex?"

[PerverseConverse]

I have a form for my child's new school which asks me my child's gender. I feel it should say "sex" seeing as gender is a social construct. Would I be wrong to cross out gender and write sex?

I did this on my contract for my new job yesterday.
Just said I've not got a gender, crossed it out wrote sex and female.
Then had a little panic about it.
Im sure it will be fine, I think contract stays in house, might get scanned and sent to head office.
Either way what I wrote is correct and I would be happy to explain if asked about it.
Will definitely need to be more careful about what I'm posting now I'm working for a big company.
There's a social media policy in the handbook, not read it yet.

I cross out gender each and every time and write biological sex in its place. Most of the forms relate to NHS treatments anyway..in which case they should 100% not be asking about performativity and dress preference...

My kids are primary school aged; they shouldn't be doing, thinking or performing gender yet. Let them just be who they are.

The gender vultures can back right off my kids bodies.

I did this recently when I joined a new library near work. In Islington, which seemed to say it all...