Just wanted to draw them together, I really like this characters, and both are voiced (in Germany) by Sabine Bohlmann, my favourite Voiceactor with the cutest voice in the world.
Hope you like it. ^^
Isabella Garcia Shapiro from "Phineas and Ferb", Lisa Simpson from "the Simpsons".
Just to make clear: usual I would never crossover PnF with Simpsons. I just draw them together because of the voice actor.