Tulivu: I have a 1 yo pony lover who is encouraged by my MLP loving wife, so what do I need to know?
Incredibly simplistic plots but with consistent characterization (though not actions), some good dialogue, great voice acting, and some cute songs thrown in here and there.
Twilight Sparkle is the brains of the operation. Every episode ends with her telling this princess what she learned about friendship, which are overly simplistic messages, but hey, it's for 4 year-old girls. She has a little boy dragon helper, named Spike. He's incredibly boring.
Rainbow Dash is the tomboy. She likes to go fast and take action.
Pinkie Pie is random, and because we're dealing with children, random is supposed to be funny. She does have some good moments though.
Rarity is the fashion loving stereotype. Pretty much Sex and the City wrapped up into a package for little girls, wanting a prince charming and all.
Fluttershy can't talk above a whisper, she's meek and shy and loves animals. I suspect that if this were meant for teenage girls, she'd be cutting herself.