If you'd like to see some HC gameplays using high streaks including a few that used Sentry guns and didn't result in getting kicked for TKing, just click on the thread below:
There are several examples in there for you to look at. I myself have only gotten kicked from one HC game (not from streaks btw) in 31+ days of playtime. I have never gotten probation for it. So as much as you might protest, your issue really does have to do with your playstyle. Some simple adjustments and you'll find that probation really isn't a problem.
There is no rating in America that does not allow the kids to buy or play this game.
Technically (legally), you might be right. But...
Do video game retailers support and enforce the ESRB rating system?
While the ESRB does not have the ability to enforce its ratings at the retail level, it does work closely with retailers and game centers to display information that explains to customers how the rating system works. Moreover, major retailers have established their own store policies requiring age verification for the sale or rental of M (Mature) and AO (Adults Only) rated games, and ESRB actively encourages and supports these efforts. The most recent mystery shop study conducted by the U.S. Federal Trade Commission (FTC) found that national retailers enforced their store policies by refusing to sell M-rated video games to customers under the age of 17 87% of the time. The ESRB Retail Council (ERC) also conducts regular mystery shop audits and finds similarly high levels of compliance. (empahsis added.)
So, practically speaking (which is all that matters), in America kids are NOT allowed to buy the game.
Not too many young kids walking to their nearest game store to buy something without a parent. So while the technicality of ESRB enforcement does exist, it's negated by circumstance. And there is no law against parents allowing their children to play CoD in the US. Therefore, despite other countries restrictions you will continue to find children online playing CoD.