孩子们在操场上踢足球（换成英语）

在这里面，没有必要强调soccer吧。
Children are playing football on the playground.这样是普遍用法。
KICK也没有必要吧，KICK是强调的一个动作。。。是纯粹地“踢”，没有人会有事没事地把球踢，哈哈。
因为踢球是在于娱乐。所以用playing ,play 也有许多用法，如playing the piano.

Children are playing soccer in the filed.

孩子们在操场上踢足球
The children kick football on the drill ground

The children play the soccer in the drill ground

Children are playing soccer on the playground.

Children are playing football on the playground