I know I'm going to be in the serious minority here, but I did not particularly care for Ohana's character breakfast. Yes, Mickey and Pluto were cute with their leis, and Stitch was a real hoot to watch as he made his way around the room. But the food, frankly, was awful (cold bacon and eggs, warm fruit), and our service left something to be desired. I know service can drop the ball anywhere, and food can be left sitting too long anywhere as well, but we didn't find it even worth going back and trying again.
We do, however, make a point of going to Tusker House in the Animal Kingdom for their character meal, every single trip. You get to meet most of the "big" characters - since you mention Disney Jr, you'll meet just about the entire Mickey Mouse Clubhouse group at Tusker House. It's Donald (outside), with a dedicated photographer, then inside, you'll find Mickey, Minnie, Goofy, and Daisy all in safari gear. We've had good character interactions and tasty food there all the times we've gone.
If you really want the Disney Junior crew, Sofia, Doc, Handy Manny, and Jake are all at Hollywood & Vine - though with Star Wars weeks taking over H&V through mid-June, you might want to double-check that the Disney Junior crew is still there for morning meals. The CM at the 407-WDW-DINE number can likely confirm for you when you make a reservation. We normally do Hollywood & Vine for lunch, actually - the food's better than I originally expected for a buffet, and the characters are normally still there at lunchtime.
We keep meaning to try Garden Grill at EPCOT for their character meal with Chip and Dale + Mickey and Pluto, but it's only available at dinner... and to be honest, there are lots of other EPCOT restaurants that we love to eat at. We just can't make ourselves prioritize this over Le Cellier, for example.

I've heard good things about it, though!
Chef Mickey's is sort of the classic character meal, but it's likely to be booked solid on such "short" notice. It's also very busy and loud... but that's part of its charm, I suppose.