PillowFight/Assets/Scripts/Child.cs

using UnityEngine;
using System.Collections;

[RequireComponent(typeof(Rigidbody))]
public class Child : MonoBehaviour 
{
    public float Speed = 10f;

    private Rigidbody _rb;

    void Awake()
    {
        _rb = GetComponent<Rigidbody>();
    }

    public void Move(float xValue, float zValue)
    {
        // We move the child depending on the camera orientation

        Vector3 forwardDir = Camera.main.transform.forward;
        Vector3 rightDir = Camera.main.transform.right;

        forwardDir.y = 0f;
        forwardDir *= zValue * Speed;

        rightDir.y = 0f;
        rightDir *= xValue * Speed;

        _rb.velocity = forwardDir + rightDir;
    }
}