[2021] What does child spawn mean? And how do I set that a vehicle spawns after it get's destroyed.

Spawn tables use a parent-child hierarchy, which is a form of relational model. I suggest looking up object-oriented programming if you want to better understand where the terms come from and how they're used. It has nothing to do with biology, and it has nothing to do with multiple items spawning together.

For the purposes of what you're looking at, parents are the table. Children are sub-tables or the actual individual asset. Assets are always children in this case, but tables can be either or both.

When you place an item spawn node on a map, that spawn node is referencing one of your tables. When the game tries to spawn an item, it looks at the children of the table, and randomly chooses one child to spawn. If the game randomly chose a child is also a table, then the game will go into that sub-table and choose repeat the process. This process repeats until the game chooses a child that is also an actual asset (e.g., an item like the Eaglefire).

Children have weight, which influences their chance of being randomly chosen. The higher the weight, the more likely it is to be chosen. The lower the weight, the less likely it is to be chosen. How likely is likely? Add up all the weights of the children in a single depth together, and then divide one child's weight by that total weight. This is your percentage (in decimal form).

There is no "cooldown" in spawn tables. For vehicles, they will spawn up until the max limit for the map (editable from the gameplay config) has been reached. For items, the cooldown on how often items spawn/respawn/despawn is determined by your difficulty settings (the gameplay config). You do not influence these things from your spawn tables.