Depends on why you don't want mature themes, I can give you mature games too. Not every rated M for mature comes from "Call of Duty" syndrome. Games like Catherine just deals with a mature theme despite its puzzle game mechanics, or games like Demon's Souls or Dark Souls are mature mainly for its hack-and-slash action elements.

Anyhow, my list of stuff:
Disgaea 3/4/D2 are all entries into the sRPG genre. All of which are fairly similar in terms of its mechanics: strategy RPG with a heavy element in random dungeons and power leveling. The stories tend to follow a demon around or someone who wants to defeat a demon. Characters tend to be over-the-top and generally are hilarious. For example, one of the "badass" demons in Disgaea 3 volunteer and follow the school's rules (whereas honour students are the ones that don't follow school rules).

Tales of Xillia is a fantastic action RPG, with its second installment coming soon on the PS3. The game follows a story of 2 characters who met by chance, a young medical student Jude and a mysterious enchantress Maxwell. It's like playing Final Fantasy with the combat system based around hack-and-slash elements, with quick combos. I grew up on Tales of Symphonia (also on PS3 as a remastered game), so I've been a fan of the series. Tales of Graces f is a slight departure from the Tales formula, but is still enjoyable.

Eternal Sonata: a story that follows Chopin in his dying moments, dreaming of a land from afar. Chopin meets Polka, and they have an adventure. Strangely positive despite you know that he's dying. The mechanics is interesting with the use of light and shadow, where monsters and characters get different properties over time.

Hyperdimension Neptunia (and mk2): Cute anime girls in RPG about a place called gamindustri (Game Industry), with each console system represented by a cute girl. Cute anime girls RPG.

Portal/Portal 2: FPS meets puzzle game. That's basically it.

Valkyria Chronicles: Set in WWII in a fictional world, you play an sRPG game where your units are your military men, with different classes and gun power. The game plays like a cross between turn-based strategy and real time movement/shooting. The story is engrossing and the mechanics are solid. A true gem in the rough for a Japanese game.

Dragon's Crown: In short, Diablo 2 loot system meets a beat 'em up game. you travel through short dungeons like a final fight game with 6 classes, and then get loot, which lets you beat 'em up more, and get more loot. Just like Diablo! The artwork can turn you off though.

3D Dot Game Heroes: Think a cross between Minecraft artstyle and A Link to the Past gameplay.

Resonance of Fate: Interesting JRPG formula.

Fighters include: King of Fighters XIII, Ultra Street Fighter IV, Blazblue: Chrono Phantasma, Aquapazza, Soul Calibur IV and V, Tekken Tag Tournament 2, Persona 4: Arena Ultimate.