This stranger heard we were planning for my daughter's fifth birthday,
我们正在为女儿的五岁生日做准备，一个陌生人听到我们的交谈

and volunteered to drop off
自发提出要放下自己的事情

and set up a commercial bouncy house (that the kids loved)
要帮我们做一个游乐场里的那种充气弹跳床（孩子们都特别喜欢的那种）

and he wouldn't take a cent in payment or let us help.
他不愿意接受任何报酬，也不用我们帮忙

He just told us to play it forward.
只说让我们在生日聚会开始之前，可以提前玩一下

I was blown away by his generosity
我为他的慷慨和善良感动不已

and it was a lot of work to set up and pack away
搭建帐篷，收拾工具花费了他很多的时间精力

and he just said he likes knowing that kids had fun.
他说，他只是喜欢孩子们开心玩耍的样子