Question

the children will sing for their parents对吗？

Answer 1

the children will sing for their parents对的，没有语法错误

Answer 2

the children will sing for their parents.
正确无误。
意思是：
孩子们要为他们的父母唱歌。
也可以是：
the children will sing to their parents。
意思是：
孩子们要对他们的父母唱歌。