"Paradise", in this case, is the abode of the gods, and the gods are the audience of the theatres of the Boulevard of Crime (so called because adultery and murder happen in the theatres ever night). Thus, the "children" are the actors, writers and producers of the stage who cater to these "gods", their whole lives revolving around the pleasure of the audience.
This film is spoken of by some as the greatest French film, and it's epic scale, intermission and grand credit sequences indicate that it wants to be seen as an important film. I am sure it is important. It has it's significant place in the history of cinema. But as a whole, I am not sure I want to give it too much credit. It is good, the characters are well-drawn and it uses it's length of time well, but I do not know how much I will consider this film in the future. It has to do with show business and with romance, and the presentation of both are far removed from my own experience, nor does it teach me much about the context. The acting is an older style, almost vaudevillian, that keeps me distant from the characters, even as I am somewhat involved in their stories.
Yes, it's three hours. But it is certainly a significant watch, and a generally enjoyable one.