No.
Just no.
I have already had issues with my son getting upset because his best mate said he was a girl because he has long hair. My son is very resilient on this and was adament he is a boy because he has a willy. I still had to reassure him it was OK to have long hair if he liked it that way and lots of famous men had long hair. And we've had conversations over pink being 'for girls' too. I had to point out his daddy likes wearing pink but he's definitely a boy (his dad does like pink).
DS is frequently a dinosaur.
He's a clever boy but he simply lacks the capacity to understand this stuff at age 5. I've already taken a conscious decision to distance myself from my family because it was causing me distress and him confusion at home. Its a subject we will have to broach at some point but I do not understand why this might be taken out of my control and before he has the maturity to deal with the subject properly.
This isn't a game. This is the reality of some peoples lives and its a deeply complex and adult issue.
5 year old need to understand both sex and gender and difference between them to properly understand the concept of being trans and they need to understand the issue of stereotypes and how not everyone conforms to stereotypes in order to be able to know the difference between being non conforming and trans.
Otherwise you are just going to erode boundaries which protect kids on the basis of sex and you are going to confuse the hell out of them.
This is so wrong. It smacks of adults putting their own needs and political agendas ahead of the cognitive and emotional development of children and their understanding of the whole. That is a massive safeguarding risk of its own right there.