1.the large amount of money will be in vain。（要用be 吗？）
2.some people hold the idea that sending their children to art classes will add the extra chances of (还是用for或to?) success in the future.
3.Art classes can help children to learn more and to be more likely to win in the fierce competitions.
4.it's well known to us that all the students should attend the college entrance examination, but if they are art students,they will have a big edge over other common students.
5.Others hold the opinion that sending their children to art classes will cost too much,and if their children are not really interested in it,the large amount of money will be in vain.
6.Also,it will make children feel so tired and stress out,so it will do harm to their health.(还是用is bad for /is not good for their health更好？）
以上六句，麻烦大家了
太感谢了，但是我还是有一些疑问,麻烦您再指导一下哈
sending their children to art classes will cost too much （后面的那位同学说cost too much 后面要加money，但是我觉得不加好像也行啊？）
如果换成你建议的用法就是...and have an advantage in the fierce competitions这样吗？
对啦，还有some/many/most people,后面的动词是不是都用原型啊，比如 some people think that 还是用 thinks that?
【1】其实可以不用加，因为耗费的不仅仅是money还有精力等等。不加money范围更宽泛一些，意思更多一点。
【2】Art classes can help children to learn more and have an advantage in the fierce competitions.
【3】用some people think that。前面主语是复数。