Until proven otherwise. And honestly, where is the 'national security' risk? There is probably far more data available in public databases that China could gather and analyze, not to mention you can apply the same paranoia to other services US and foreign.
The children are not choosing to do so in any meaningful sense, no. But anyway, most of the families are filing for asylum, which is legal. They aren't entering illegally; they are filing for asylum at the border. We're the ones choosing to cage them instead of treating them more humanely.
And it's not sensationalist to speak the truth. There are plenty of photos and videos. We are actually doing this.