need help on helping child with autism about body changes??

my 7 year old boy is autistic and we finally got the diagnosis.

I have been doing my best as i possibly can as his only parent but i am way out of my depths with this one slight problem..

as he is getting older, his body is changing but i am not sure how to explain or show him that it is okay and normal. he is still in nappies as he is unaware he is doing it.

i will be talking to his nurse on how to approach this but would love some feedback on how else i can also make him comfortable with the changes and if anyone is going through the same thing?

much appreciated.