The do not enter sign could be aimed at civilians with the enter only aimed at whoever is authorised to go in. It's not misleading at all.

op never said which sigh he disobeyed she could have just stood their

Use your brain please. Thank you.

lol for real

Airport security is pretty nuts in any major airport. I dont happen to know where OP landed, but I'm guessing that's what happened.

If you take a camera, lube, ******, and peanut butter into the wrong bathroom, I wouldn't be surprised.

In America it is illegal to use the bathroom other than the one that matches your legal gender. IE if you were born physically male you use the men's restroom. If you were born physically male but have had a sex change and legally changed your gender to female, then you use the women's restroom. If you were born a woman you use the women's restroom. Whatever your LEGAL gender is that is the bathroom you use. You CAN and sometimes WILL be arrested if you go against this law, depending on how much the other people in the bathroom whine and complain ;)

But there were two signs. That doesn't even make any sense

The sign probably meant "Entrance Only". Either you read/remember it wrong, or the sign was misleading. Any time a door says "Do Not Enter", don't enter regardless of other signs. Still, it does seem a little excessive to be arrested.

so you will arrest a little boy who goes in the women's bathroom with his mom?

Misgendered children (girl goes with dad or boy goes with mom) in public restrooms is usually not an issue for smaller children.