i second CGRetired, maybe not getting the motor running is a blessing in disguise! unless your grandson has some experience flying RC airplanes there is no way that your gift will last longer than its first flight. in fact the next post you'll do is "how to fix foam that has been broken into a thousand pieces".

but if your grandson does have some flight time, there is usually a safety mechanism with these ESCs. for example, you'll need to go to full power, back to idle THEN hit the red button in order to get the ESC to engage. since there is no manual, what it is difficult to say. try that first. this prevents you from turning on your plane with wide open throttle (WOT) and chewing up anything in its path.