This may just be a perfectly normal development issue and he may well grow out of it. However, having had a DS who received speach therapy for three years, I think you should ask for a refferal to see a SALT. They will assess your DS and tell you if they think he needs help. They may decide to just keep an eye on him but in the meantime be able to give you some tips on how to encourage the proper use of sounds
Thanks for replying, and for the reassurance. I think I will track down SLT and see what they think. Compared to all his friends the same age he does seem to be behind with these sounds, and they all talk very clearly. That link was very helpful though, thank you.
DD2 is exactly the same age and has exactly the same problems. We asked at her pre-school and she was assessed by the SALT that comes in there and she said it was all entirely normal. We've been concentrating on individual sounds and combinations that she finds difficult, we started with 'bl' and just split the sound up so 'blue' becomes 'b-lue' she now does this one fine (unless she's talking soooo quickly she forgets). We're now doing the same thing to other sounds and working up to trickier combinations such as 'sn' and 'str'. She also can't do 'ch', 'sh' and 'th' but I'm leaving them for a while as I think they tend to come a bit later anyhow.
Good heavens this makes me feel I must be excessively laid back. I always considered my son, now 3.9, reasonably well-developed speechwise but now I wonder if I too shouldn't get him assessed. He said "prums" for plums for ages & still says "Puffenee" for Putney and "horns" for prawns. And of course "fink" for think etc but then plenty of teenagers round here do that. I've always thought it rather sweet, something I'll miss later on and embarrass him with when he's older (not the teenagers, of course, that's just sad).
marytuda, I think my DS is reasonably developed speechwise as well, but there are just a handful of sounds he just can't do, and gets very frustrated at not being able to say them. I'm reasonably laid back as well, but having listened to his friends and younger cousin, they all seem to be able to make these sounds without trouble.
I've read somewhere that if there is a problem that it's much easier to sort out at a younger age when the bad habits haven't become too ingrained (probably not phrasing that correctly, but hopefully you know what I mean)
I found my local SLT on the NHS website (after mistressploppy suggested it), there's a number I can call and I can self-refer, so I might do that if nothing improves soon.