Dear S.N.,
If the older children were going simply to grow out of the /r/ problem, that would much more than likely have happened by now. Let them have the therapy. Ask the speech/language pathologist how you can help, and do all that you can.
The time to deal with this trouble is now. When people hear an adult with a pronunciation problem, they unfortunately may tend to judge the speaker critically. An /r/ problem in an adult is sometimes wrongly interpreted as a clue to the speaker’s maturity or intelligence.
Many five-year-olds do grow into the /r/ sounds. Still it would not hurt to teach the child to discern the difference between a correct /r/ and your 5-year-old’s version of it. You can call /r/ the 'Growling Sound',' and refer to the correct /r/ as the 'grown up' way to say it--avoid suggesting that your child's speech is 'wrong.'
With older children, I refer to the error sound as the 'old way' and the correct sound as the 'new way.'
Learning to discern correct /r/ sounds is good auditory skill development and appropriate for age five. Ask the speech/language pathologist for guidance.
Best Wishes,
Ruth Alice Jurey, M.S., C.C.C.
Speech/Language Pathologist