It's dangerous to leave children alone at home.（形式主语的句子,避免头重脚轻）
= To leave children alone at home is dangerous.
=Leaving children alone at home is dangerous.
It's dangerous to leave children alone at home.（形式主语的句子,避免头重脚轻）
= To leave children alone at home is dangerous.
=Leaving children alone at home is dangerous.