They are both 18 y/o with tremendous upside. You're probably right though, Wiggins hasn't fully grown into his body yet and Parker seems like a man child. Not quite Lebron status but pretty close IMO.
Who would start at the 3? Outlaw? Williams? Acy? Gay is the best player of the bunch. Do the Kings need more wing scorers? Probably not, but I do think he will help down the stretch this season. I'm not saying they are gonna make the playoffs but they will definitely be better than they were...
Wiggins is good, but Parker is much much better at this point. Don't get me wrong they're both really good players but if I had to choose between Wiggins and Parker I'd most definitely go with Parker.