My youngest grandson is nearly 4 (in May) and although we could understand him, when he started at the nursery last September, they were concerned about his speech levels and suggested a speech therapist. He has just finished a course of 6 lessons, one a week, and although he`s still not great, his speech has improved a little, and he`s now stringing sentences together. My DIL is a little bit touchy, but eventually came round to suggestions by the nursery teacher, but if your DIL is really unapproachable, then maybe getting your son on side will help?