Turns out one of the downsides of an autocratic hereditary power structure that brutally oppressed millions of people for hundreds of years is the heirs to said power structure are fair game when the oppressed rise up. Like it or not, royal heirs are a threat to any nascent socialist revolution and a figure for reactionaries to rally around.
Also I just want to mention in this very time period the very same royal family had spent years feeding millions of people to machine guns and artillery, and no small number of civilians, including children, were victims of that war too.
When our turn comes, we shall not make excuses for the terror.
In other words: 
No half measures Walter
we love our admins, we have the best admins! Everyone is saying it, I have posters coming up to me, big strong posters, we have the best posters, they say to me
Plenty of monarchs have been crowned younger than that, it's an inherent part of monarchy as a system. The nobility recognizes this and has no trouble with eliminating heirs or potential claimants. But when the oppressed do the same people are up in arms about it
In the middle of a civil war that was still very much undecided. In a more favourable situation it would have been better to do what the Chinese communists did with the last emperor, who coincidentally was crowned when he was 2, by reeducating them. But the Bolsheviks didn't have that luxury.
Of course, Russia was never ruled by women
Like it or not, moral or not, whatever, monarchs and their heirs are legitimate targets for revolutionaries. I won't cry over dead royals. Boo fucking hoo, they literally lived like kings and got what was coming to them.