Háizimen kuàikuàilèlè de zài cāochǎng shàng wánshuǎ.
The children played happily on the playground.
Tips
grammar
快快乐乐 is a reduplicated AABB form of 快乐 (happy). This reduplication intensifies the feeling and adds a lively, vivid tone. Common in speech and blessings.
