You may enjoy it much more than the game deserves.
Story mode is mediocre to say the least... bad camera and wonky controls... although my 6 years-old likes it quite much, but only in single-player mode. Co-op mode is plainly broken, several platforming sections becoming completely unplayable... as a matter of fact, the game should have never been released this way. You will be very disappointed if expecting a game à la Lego Star Wars to play together with your small child.
Battle mode is much more satisfying, and the camera and control problems become much less noticeable... however you will have to play Story mode a lot in order to unlock all the scenarios and characters. To be honest, I have had a lot of fun playing Battle mode for much more hours than I would like to confess, and not only with my child... It is a guilty pleasure to experiment with all the different combo attacks / takedowns of each character, environmental events, battle modes... playing as Spider-Man vs. 3 CPU opponents... and so on. Not that this mode is perfect either: fight is a bit unbalanced, some scenarios are rather ugly, and not all characters look as cute in close up. However... you might be surprised to enjoy this game much more than it deserves.