开心自在用英语怎么说

"开心自在"用英语可以说成 "happy and carefree"。

来源："开心"是汉语中的 "happy" 的意思，"自在" 是 "carefree" 的意思。

下面是一些例句：

The children ran around the park, happy and carefree. (孩子们在公园里自由自在地跑来跑去。)
She spent the day lounging on the beach, happy and carefree. (她在海滩上悠闲度过了一天，心情开心自在。)
He lived his life happy and carefree, not worrying about the future. (他过着开心自在的生活，不担心未来。)