The new policy was enacted in May. https://www.justice.gov/opa/speech/attorney-general-sessions... The policy refers all cases of illegal crossings to prosecution. Previous "zero-tolerance" policies have been enacted, but they did not apply to families which would be broken up when the adult(s) were prosecuted.

Edit: I might as well mention here that a 1997 court decision in Flores v. Reno (which you should Google for details) (yes, that goes back to the Clinton administration!) limits detention of children to 20 days even if you house them with their parents. This new EO doesn't even mention that decision so this will probably be immediately challenged in court.

The law has been consistent for several administrations. The president decides whether (and how) to enforce it.

Prior administrations chose not to enforce it against families, which meant those presidents didn't separate families.

Trump broke that tradition by enforcing the law against families.

Due to the limited resources available to immigration enforcement, all presidents must choose whom to pursue or not. Previous presidents chose to focus on violent criminals and drug traffickers.

A quick google search suggests that is not true. I'm curious where you heard that.

http://www.politifact.com/punditfact/statements/2018/jun/19/...

Can you explain what you mean? When did Obama's administration create a policy of separating families?