Explaining erection to 5 yr old boy

[Doing my best]

Are there any books that can help me/DH explain this in terms he will understand?

This morning the poor little thing said 'i feel strange mummy' I asked what kind of strange (actually thinking his sore throat got worse), and he said 'behind my willy feels really odd', then proceeded to sit on toilet for a poop and screamed it did subside very quickly, and he thinks his need to poo caused it. (His words to me, I didn't tell him that)

I have noticed he has had an erection in his sleep before, but it has always gone down before he has woken, so as far as I am aware, it hasn't worried him in the past..

DH is very technical in things, and has trouble explaining things in a simple term and amount kids need to know, so really need help on how to explain this..

[Ca Plane Pour Moi]

My DS had a similar issue when younger, came to me in tears one morning because "my penis won't go down".

I told him it was ok, it was normal and when he relaxes it will go down again. That worked and he was happy about that. He had no further questions. He was just worried that there was something wrong.

[Mildez]

My DS is only a baby but if I was in that situation I think I would keep it simple and say its normal and that's how it grows as his body grows. More details can be explained as he gets older. There are books out there but I find a lot of them have too much details for my liking for a young child.

[Livinthedream]

We just explained to DS that it goes away if you leave it alone, that all he needs to know for now.
He is rather proud of his "big willy" though