小孩玩火是危险的用英语是：Children playing with fire is dangerous。
1、play with fire=玩火，轻举妄动，做危险的事情。
例句：
It's dangerous for children to play with fire.
对孩子们来说玩火是危险的。
Be careful with that knife! You are playing with fire!
小心刀！你这是在冒险。
You'd better stop playing with fire.
你最好别再冒险了。
You play with matches, you get burned.
你玩火就容易烧身。
2、catch fire=着火
例句：
Keep your coat away from the flames, or it will catch fire.
你的外套离火远点，小心着火。
Dry grass and trees easily catch fire.
干草和树很容易引起火灾。
With so much dryness, so many communities to catch fire, so many fronts to fight, it becomes an almost incredible job.
干燥度如此之高，加上许多社区着火，有这么多前线要去战斗，这几乎成了一项不可思议的工作。
The blast caused several buildings to catch fire.
爆炸导致了几个建筑物起火。
3、come under fire=遭受批评
例句：
The government has come under fire for its decision to close the mines.
政府因其关闭矿井的决定而遭到了抨击。
The health minister has come under fire from all sides.
卫生部长受到来自各方的责难。
Share options and pensions may also come under fire.
期权和退休金也可能受到批评。
James came under fire in the office after he wrote a very critical article in the company magazine.
詹姆斯在公司的杂志上写了一篇很有批评性的文章后，在办公室受到了攻击。
4、hold fire=延缓作决定
例句：
We should hang fire until the general situation becomes
clearer.
我认为我们还是等总体局势更为明朗之后再作决定为好。