Adventure time (探險活寶) and other cartoons with mandarin dubs and subtitles
It might be hard to find the show with simplified Chinese - according to this wikipedia, the Beijing government banned Cartoon Network in 2000. Thus, the company might start to focus on Freedom China (ROC, currently in and known as Taiwan).
However, there should be some way to get simplified Chinese caption. If you're lucky enough, you should be able to grab some traditional Chinese subtitle and turn the traditional characters into simplified ones with handy tools on the Net. (OS: Some of the tools rely on Google Translate, so 95% of the result should be correct, while it sometimes mixes some characters.)
By the way, I didn't try it yet cuz I'm doing in the other ways around - I'm a Chinese Taiwanese, so I'm looking for cartoons with English caption. ️

If you're looking for some other Chinese cartoon, I will suggest you 《喜羊羊与灰太狼》（《喜羊羊與灰太狼》，xǐ yáng yáng yǔ huī tài láng，ㄒㄧˇ ㄧㄤˊ ㄧㄤˊ ㄩˇ ㄏㄨㄟˉ ㄊㄞˋ ㄌㄤˊ，Pleasant Goat and Big Big Wolf） and 《熊出没》 （《熊出沒》，xióng chū mò，ㄒㄩㄥˊ ㄔㄨˉ ㄇㄛˋ，Boonie Bears）. Though the former in 2005 and the letter in 2012 are made by a Mainland Chinese company, they are my childhood and almost everyone in my high school can still remember its theme song.