My almost 5 year old son can't pronounce some letters properly. " ta", "ra", "ka" are the letters to be more specific. Although he tries to pronounce "ta " and "ka" and can pronounce them although not very clearly, but he is not able to pronounce "ra" at all. We have taken him to speech language pathologist twice, once when he was 2 yo and once when he was 3 yo but no major problem was pointed out with him and he started speaking at 2.5 yo. Is lisping common in children of this age or should we go for another evaluation.