Why was it okay when Obama did it?

It wasn't "okay", but he didn't do it as much.  Obama only did it with a few children; Trump did it with many more.

Also, the great became great during the Obama Presidency, after the Bush disaster.  It improved less under Trump than any President not named Bush in almost 40 years.

Anything the DNC does, thinks, or says is praised by the media.

Trump piggy backed off of Obama’s successful economy and you trumpets keep thinking it’s all Trump’s doing you must be too young to remember Bush’s recession and how Obama cleaned it up, regardless the economy is in the tank now with tens of millions fired the last few months alone.

It was not okay when the Obama Administration did it either. People protested Obama's handling of the immigrant situation as well. Funny how Obama deported more iIIegaIs in his first few years than Trump but conservatives didn't actually care. Conservative propaganda like Fox News tried to spin it against him and called him "Deporter in Chief". But Obama did great for the economy. Unemployment was reaching 10% when he came into office, and he brought it down to about 4.5% by the time he left. We were still seeing the momentum of his economic policies before Trump's bIunders. He also introduced his economic stimulus plan when he first got into office and ended the Great Recession. We saw GDP grow the very next fiscal quarter for the first time in about 2 years. But ofc conservatives don't actually care about that either.

Bill Clinton started the program of putting illegals in holding areas, Bush used them, Obama used them, nobody complained until President Trump used them. It's ridiculous.

The answer to your question lies in the name of the forum in which it was posted:  Politics.

ICE existed since 2003, and US customs officers existed long before that.  Trump did (successfully) increase their numbers and give them a clear mandate to step up their operations, which is why he gets the blame / credit for the number of illegal migrants arrested.  But he wasn't the first president to support "separating families", and neither was Obama.

When an adult gets arrested, anywhere in the civilized world, their underage kids are not arrested along with them.  And if there's no adult family member(s) to take care of the kids, the kids must be placed in government custody.  That's the way it's always been, and no presidential candidate is offering to change it.  The rules for illegal migrants are exactly the same as they are for US citizens.

The left likes to completely ignore the illegal part of illegal immigration.  They act as if those people were arrested not for breaking the law, but because they speak Spanish.  

Obama only used that for 3 days. Trump is still using them even though the court ordered the people be released. Obama inherited a failing economy and turned it around. Trump inherited a growing economy and used the correction measures to juice it higher. That's the reason the economy is falling now.