DS has always been very vocal and picked up words easily so we're very lucky there. He turned 4 two weeks ago and I've been noticing that he has trouble making a "th" and "st" sound. Ex. when he says thanks it sounds like nanks. I'm wondering how much of this is normal kid speak or if it's something I should bring up to the pediatrician. I wouldn't really think much of it but he is tongue tied and sucks his thumb (we're working on that one). Does anyone else notice their preschooler pronouncing words like this?