ohhh my DS is the same and also 4 in march. He has always been complimented on his pronounciation and I was starting to get worried cause I wasn't sure if he 'regressed' or it was just a normal developmental thing.
He has problems with saying "th" sound and will often say 'v' instead of 'f' and is also saying a 'w' instead of 'r' like your LO Maya. I figured some of it he is playing with the sounds and the way he says things but wasn't sure