Either you're feigning ignorance or outright lying. Marx and Engels saw couples as breed bots whos children would be raised in collective daycares while mom and dad were obligated to work. The society and state would be in charge of education as opposed to the parents through home or religious education. Marx and Engels hated the traditional patriachal family. To state that Marx and Engels were stupid enough to think that the majority of women would willingly give up their children to the state in a post-capitalist world is ignorant and/or arrogant. The only way this would be achievable is through coercion or by creating such harsh conditions that families would essentially be forced to give up their children. To pull a page out of your book, prying children from their parents to be raised in the communist society would go against their biology and hence, unnatural. Everything in communism is predicated by violence and force. Marx didn't argue that the world would slowly and peacefilly slide into communism as it had to capitalism, he advocated for violent revolution by the proletariat. Communism fails because of its appeals to force and coercion. You can't make the "communism will be an idea who's time has come" argument when the incitement to violence against "oppressive" institutions exists.