Some of what a boy needs to know about puberty is awkward to ask, so tell him before he has to.
From the tip
In puberty, erections don’t only come when he’s thinking about sex. Childline tells boys they can happen when they’re not expecting them, at school or on the bus, that this can feel embarrassing, and that it happens to most boys. Tell him so, ideally before it happens.
See the GP if he’s worried about how his chest looks, if the pain isn’t going away, or if there’s a lump, a change in the skin, or discharge or bleeding from a nipple, and tell him the doctor will be used to talking about it.
If he shows no signs of puberty by fourteen, see the GP.
Any of this can come from his father, or from any adult he trusts. Say it side by side, in the car or on a walk, keep it short, and don’t ask him to reply. He can also talk to someone himself, without you in the room. Childline, 0800 1111. For anyone under 19 in the UK. There is a one-to-one chat online at https://www.childline.org.uk/get-support/1-2-1-counsellor-chat/. Help is free and available at any hour. A charity for young people explains puberty on its website, alongside sex and contraception, so you may want to look first. Brook. Online at https://www.brook.org.uk/parents-and-carers/. Then leave a good book about boys’ puberty where he’ll find it, and tell him he can ask you anything in it, now or later.
Tell him that sudden, severe pain in a testicle needs a hospital straight away, however embarrassing, and so does pain there with sickness or tummy ache, or pain that lasts more than an hour: a twisted testicle must be treated within hours. Call 999. Or go to your nearest A&E. Help is free and available at any hour.