Talking

My son will be 3 on the 13th. I thought he was doing fine with his speech development but my mom thinks he’s hard to understand most of the time and that he doesn’t enunciate his words well. I can understand him completely and my husband can too. He talks a lot and nobody else has ever mentioned anything about him seeming behind for his age (he goes to gym childcare and Sunday school). He does have trouble saying his r’s and l’s which causes some words to sound funny. He’ll see his doctor in a few weeks and I plan on asking her but was just wondering where other kiddos are at at this age?