Hi,
I've been lurking for a year or two and I've registered as a user so I can join your conversation!
I don't have a child who fits that description but I was once a five year with two hearing aids (and a transmitter/radio aid for the classroom). I had a bi-lateral (both ears) moderate sensorineural hearing loss at that time. By the time I was ten, I had a severe/profound loss in both ears.
I have always struggled with making friends even though I'm quite a confident person generally. I'm just at such a disadvantage in a group setting. I usually see friends 1:1 and that makes socialising so much more enjoyable for me. Most of my hobbies and interests are things I do on my own and I accept that about myself.
My advice would be to look at the NDCS links a PP posted above. I agree with the others that knowing other people with hearing loss is really important. You don't need to tell your little boy that you're trying to help him make friends with other deaf children, you can just say that you want to talk to the parents of other deaf children (and he can go and play while you do that).
At 5, I remember feeling sad about not having any friends and I felt a bit ashamed. I've always had a lot of pride so I didn't talk about it or ask anyone for help. In your place, I would try to hide any concern that you've got (in case he thinks you're ashamed of him for struggling with this) but instead support him to cultivate 1:1 friendships (e.g. playdates, etc). This might mean yourself befriending other parents in the playground but you said you're sociable so hopefully that will be straightforward for you.
Something to watch is praising him when he hears or when he copes well. It can give the impression that he should aim to 'pass' as a hearing child. It can put a lot of pressure on a child to pretend to be something they're not. It's likely adults will say 'wow, you speak so well' or 'I wouldn't have known you were deaf!' (they consider this a big compliment) or 'I can't see your aids much/don't notice them'. It's subtle but the underlying message here is 'conform to the hearing norm'. Don't misunderstand me, at the time I liked being given compliments, it's only now that I'm an adult that I can see the deeper meaning in what was said (by caring, well-intentioned people).
Despite my struggles with friendship, I was a high achiever at school and being able to easily read and write really helped so focus on those skills. I have ended up in senior management in my company as an adult but it did take a long time and was really difficult to get there. Normal life absolutely drains me.
The best thing about my disability is my hearing dog so you might want to check out their website!
I'm new to being a member here but I'm very happy to answer any other questions you have - any time.