Wow, I hate to say this but I pray this little girl isn't a victim of human trafficking. It's a very big thing in Portugal (not to mention many other places) and those creeps look for YOUNG girls.
Maybe they saw the parents leave and then made their move. You neever know. It's really sad to say but those creeps are very good at what to do.
Please god, help this little girl find her way back home safely and unharmed.