Goblin nimble escape (New GM question)

[sasigns]

In the encounter shown below the party is set for a rest at the end of a long days travel. They are being ambushed by the goblins.
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The question is lets say the first round of combat the goblins fire their arrows at the party. At the end of each of the goblins turns it can use

Nimble Escape: Goblins know when to run when things get heated. You can take a Disengage or a Hide action as a bonus action.

to hide back in the trees.

it is now the payers turn. What checks do I use to see if they know where they are or are able to attack them? Sorry for newbie questions..

[Nebs]

You can compare the goblins' subsequent Stealth checks versus the players' Passive Perception. Any goblins that roll stealth higher than the players' passive perception must be found using an Action to perform a Wisdom (Perception) check. Or, as DM, you could just have them roll for Perception.

Alternatively, when the goblins go to use their Hide. The players' could still make blind attacks at the goblins, as if the goblins are invisible, since the players will obviously know they're there even if they can't see them. This will allow casters to simply chuck things like Fireballs in the goblin's general directions.

[Zacchaeus]

The rules for hiding are in the sidebar on p177 of the Players Handbook. So the first thing is you can't hide from someone who can see you so if the Goblins can be seen then they can't hide - no matter what special abilities they might have.

So the Goblins would have to start the combat hidden before they fire their first arrow. Once they fire they can use their Nimble Escape ability to roll a Stealth check and you compare that result to the PCs passive Perception. If the Goblin succeeds they stay hidden. On the PCs turn they can use their action to actively search for the Goblins by making a proper Search roll.