Is this something which can be treated / addressed with exercises?
Is it something they grow out of?
I had speech therapy when I was six. I had a bit of a problem pronouncing 'S' (the fact that by then, I was learning my third language, ie a new language every 2 years, possibly had something to do with it) Strangely enough, I could pronounce 'ST' fine, so the speech therapist worked on that, making me emphasise the 'S' in 'ST'.
I can't remember how long I went for, but it really wasn't for very long – just a few weeks. And TBH I was a bit miffed that I was robbed of my speech impediment – for me it was mine and it made me special ! Although I'm **** glad about it now 8)
Will your boy grow out of it ? Well I don't know, but later when I went to secondary school I was amazed to discover that a girl there had the same speech impediment that I had had – obviously her's hadn't been treated. And she still had it when she was about 14, which was the last time I saw her.
Your boy will probably enjoy going to speech therapy, I did. I had a rather lovely young lady, and I can still remember one of the poems she taught me to recite 🙂