That's a scary incident! It's fortunate that the girls were not hurt from the falling glass panel. It's quite unusual for this to happen, but it's probably a good idea for building management and the law corporation occupying the office to investigate the cause - whether it was an unfortunate accident or there's some bigger issue at play.
At first glance, it doesn't seem like something that should be happening to a building structure, so it may be an isolated incident. Nonetheless, it's always better to be safe than sorry, and a quick check by the relevant authorities might help reassure residents in the estate.