Good question. How do you take a potentially volatile situation and turn it into a communication dream? Not an easy thing to do. You must be a student of human tendencies, skilled in observation and interpretation of body language, relationships and voice inflection. Or you can just take a shot. Either way, your approach must be one of timidity, humility and timing; built on certain basic principles of human interaction if you are to succeed.
Let’s look at two scenarios: The first takes place in the environment where I train. In this particular realm, let's assume that a father is training his son to squat using the so called "Smith Rack." This father's own instruction capability may be way over-estimated and he is giving his son poor advice, as well as loading the device with much too heavy a training weight. The kid could blow a knee, back, whatever. What do you do?
The second scenario is a little different; let's assume that I'm out in the field, or at the track. I see a dad having junior do repeated depth jumps from a height equal to the kid’s waist--around belt level. Oh yeah, the kid's also wearing ankle weights and holding 10 pound dumbbells in each hand. (I wish I was making this up and hadn't witnessed it first-hand)
In each scenario, the potential for unsolicited advice to blow up in your face is huge. Your approach must be tactful and humble, with an immediate solution to the situation. Since I have an established presence at the gym where I do most of my work, I am recognized and given a certain degree of leeway towards giving potentially advantageous advice. In other words, most of the folks in the gym at least know my face and are receptive to my approach.
At the track, however, it is a different story. I'm just another strikingly handsome face and statuesque physique in the crowd.
In either case, in order for you to succeed, you must do one thing: first establish a relationship. You must find some sort of common ground, make a friend, and allow them to get to know you. You must create some degree of rapport. Every good salesman will concur with this statement. Without rapport you are dead in the water. It is a well known fact, and one that I have preached for many years now: No one cares how much you know until they know how much you care!
By spending a little time getting to know Dad and establishing rapport, you can then ask him, "May I make a suggestion on what you and Jr. here are doing?" In this way, you give him permission to either say "Yes" or "No", but it has to be his decision for there to be any degree of reception. If Dad says yes, then give it to him. If he says no, walk away. Attempting to pound your viewpoint into Dad may allow you to have a say-so, but it may also have a detrimental effect the child, as Dad's anger is now directed toward him in an attempt to prove you wrong. Not necessarily, but maybe.
Establish rapport, ask permission, and wait for the reply. The formula works, it just has to be applied.
God bless,
SP