if you've ever played for honor, then you will know this from the Valkenheim in Winter level in the campaign. what it does is launches a wooden bridge across a gap and attaches to the other side. this could be accomplished by springs, and a bunch of grass planks tied together.

While cool I don't see the kids using this in the current game state. If the launch the ability to get inside the house maybe a bridge from the table to the porch is created this way or from the picnic table to the upper garden with the grill.

 

Though with how this game works I think a zip line launcher would be better. Maybe the ammo is made of bee stingers, quartzite and a splatburst. First use either loops to a zip anchor or spikes the ground the second brings up a reticle for targeting and places a anchor on the target.   Think the harpoon from Evolv3 that would trap the monster to a smaller area briefly