I'm a little over 16 (a bit over three times over) and have been able to buy my own cars since 1970. I also have 27 years law enforcement experience. And my own children (at least, I assume they are).
One of the most common fallacies in the 'civilian' world is that any cop can take on any resisting subject and physically subdue same without causing harm to either, all by himself. If he uses any force, he's a brutal bullying bastidge; If he tries and fails and/or gets hurt himself in the process, he's a p*ssy. If it takes more than one cop to do the job, they're a brute squad.
One of the most common TRUTHS about subduing someone, and I mean anyone, who doesn't want to BE subdued is that causing injury is common. If you've never been in a fight of any kind beyond a simple schoolyard pushing match, you have NO idea what physically subduing another human entails.
This 8-year-old is quite capable of resisting being subdued; Just how much resistance he can put up is up to him, and he is only limited by his pain threshold--which, by the way, is what 'subduing' someone physically means: Finding out how just much pain they're willing to endure to avoid being subdued. A stubborn, angry child can choose to take an awful lot of pain, or go to the extent of suffering a greenstick fracture of a limb in a frenzied tantrum where mental control has been lost.
I have to admit, being 'sprayed' is a miserable experience. It passes, within minutes. Getting a dislocated shoulder, a broken arm, or fractured wrist is likewise miserable, and takes a lot longer to 'pass.'
You choose--you want me to grab your little hysterically-struggling darling and tie him into little knots to calm him down, or give him a little dose of pepper spray that takes his mind off the tantrum (and pointed stick) and inspires him to peaceful cooperation?
I go with the pepper spray.