Can server scripts modify Player's Children?

With filtering enabled on, will i need remote functions and events to modify the children of a spawned player class type?

No, you don't need events if it's a serverscript.

When a LocalScript modifies an object in the game, the change will be made on the client, but will not replicate to the server. For example, if a LocalScript creates a part, the part will only exist on that client's data model. The server will reject the change and not replicate it to the other clients. This makes it possible to create local parts.

However, you can replicate these changes through RemoteEvents and RemoteFunctions.

Basically, if FE is enabled:

server can communicate to the client freely (server > client)

however, client has to use events or functions to communicate to the server (client > server)