it isn't child's play.; sth. not to be taken lightly
Example Sentences:
1.
Every general and every soldier was conscious of his own significance , feeling himself but a grain of sand in that ocean of humanity , and at the same time was conscious of his might , feeling himself a part of that vast whole 人人都觉得正在完成一项非同儿戏的意义重大而庄严的事业。每个将军和士兵都觉得自己非常渺小，也意识到自己只是这个人海之中的一粒沙土，而且也觉得自己强而有力，也意识到自己是这个浩大的整体中的一部分。
