speech problems in 4.8yo - when to worry / get referred?

[DestinationUnknown]

ds is 4.8yo, bright and articulate. But he still has problems with his speech and it's getting to the point where I can't always understand him first time. This is what I've noticed:

Problems with sh th ch -
Says "sop" instead of "shop"
uses "f" for 'thin' th,
uses "v" for 'fat' th
says "watch this" but it comes out as "what's this" (v confusing!)

Also - he doesn't directly substitute "w" for "r" but hasn't got a full "rrrr" sound, more a "wr" sound if that makes any sense.

Will it come naturally? He speaks fast, has lots to say and a big vocab. As his ability to use more complicated grammar, tenses etc grows I worry that the problem is going to create more frustration.

He can say the sounds sh, th, ch in isolation if he thinks very hard and tries but loses them as soon as they are part of a word.

Any thoughts welcome please!
Thanks

Ds (4.6) has speech therepy and he does all the above and more. I think s instead of sh is normal, f instead of th is normal (at his age) not sure about v instead of f.

If he can say them in isolation then it means it's coming, so probably nothing to worry about.

Don't make him repeat the words. But model them for him.

The best thing to do (imo) is speak to the school. A lot of schools have a speech therepist to come in, and s/he may be able to do a basic assessment in school for him if they think it's a good idea. If you're not happy with their response ask the GP to refer him. They may want to do a hearing test first to rule hearing issues out.

My feeling is that it is normal for now, but he should be developing it. But if he can say them in isolation there's a reasonable chance it will come without intervention.

Thanks DeWe that's helpful. Will see what teachers think.