部屋の外に子供達がいます。
There are children outside the room.
子供達は部屋の外にいます。
The children are outside of the room.
That’s what each sentence sounds like to me.
Children in the second sentence are the children, whose existence you acknowledge. Maybe you know them personally. Even if you don’t know them, you at least know there are kids around there.
What it matters in this sentence is the particle は and が (rather than word order), I think…as if I switch the order and say 子供達が部屋の外にいます。, it still sounds natural and its meaning remains as “There are children outside the room.”