It's kinda pointless question, we don't know why he chose 2 instead of 1 or 3. But he did the right thing, investing in his kids future, that's for sure.
Let's assume you are not limited in resources. How much would you buy for your children?
I would buy 2.625 bitcoins for each of them. How about you?
Why 2.6? Is this number important to you somehow? If you aren't limited in resources, you should buy unlimited amount of bitcoin, right?
Bitcoin cannot be printed like fiat money and it doesn't succumb to inflation. If we take these two aspects into account, we come to a conclusion that bitcoin is superior to fiat when it comes to saving money and possessing inherent value. Having unlimited amount of fiat money means you can spend it all to buy a limited amount of bitcoin, but that limit is only in the amount of bitcoin available for sale.
Good question. Strictly speaking, Bitcoin can be "printed" by changing just one line of its source code. And if 51% of miners reach a consensus around this version of Bitcoin, we could indeed increase the maximum supply to 30 million or 50 million. So, why is the number 21 million significant? Is it your religion?
Thus, if my resources were unlimited, my optimal bet in this game would be 0 (zero) Bitcoin. I wouldn't buy any Satoshi. Instead, I would simply purchase 51%+ of the mining power and increase the supply of Bitcoins in circulation by changing source code. This way, I could make you sell all your bitcoins for penny, and then I could easily decrease the supply again to say 21 million. This is called a strategy.
Basic C++, kids
/** The amount of satoshis in one BTC. */
static constexpr CAmount COIN = 100000000;
/** No amount larger than this (in satoshi) is valid.
*
* Note that this constant is *not* the total money supply, which in Bitcoin
* currently happens to be less than 30,000,000 BTC for various reasons, but
* rather a sanity check. As this sanity check is used by consensus-critical
* validation code, the exact value of the MAX_MONEY constant is consensus
* critical; in unusual circumstances like a(nother) overflow bug that allowed
* for the creation of coins out of thin air modification could lead to a fork.
* */
static constexpr CAmount MAX_MONEY = 30000000 * COIN;
But since my resources are limited, my strategy is to hold 2.625 bitcoins and never sell them. Basic game theory, kids.