应该填介词on，意思是：孩子尽力地照顾好他们的母亲。

hand and foot:

ad. 手脚一起, 完全, 尽力地

例句与用法:

1. He seemed to expect to be waited on hand and foot.

他像是想要人尽心尽力伺候他.

2. At home the boys never lifted a finger. We girls had to wait on them hand and foot.

在家里男孩子不动一根手指头，我们女孩子得替他们做这做那。

3. Mary has no idea how to bring up her children to be independent and self-respecting; she waits on them hand and foot.

玛丽不知道如何教育她的孩子独立自尊。凡事都是她自己替他们做了。

4. He seems to expect to be wait on hand and foot.

他像是想要人尽心尽力伺候他。