Stop pushing each other. It's dangerous because you'll bump into other people/children.
Stop messing around. It's dangerous. You'll bump into other children and knock them over.
「お友達を押したりしないで。周りの子にも危ないよ」= Stop pushing each other. It's dangerous because you'll bump into other people/children.
※「bump into = ぶつかる」
他には、こちらの言い方も使えます。
Stop messing around. It's dangerous. You'll bump into other children and knock them over.
(遊ぶのをやめて。危ないから。他の子供にぶつかったり倒したりしてしまうよ。)
You don't want to hurt other children, do you?
(他の子供に怪我をさせたくないでしょう。)
You are getting in everyone's way.
(邪魔しているよ。)