Hey there! I think its admirable you are trying to get your 4.5yo to keep their room clean, but IMO kids that age need quite a bit of help. Rooms don't get messy on their own or quickly - it takes time to pull out every single toy you own LOL! I would suggest you make the tidy up a game and as MD says break it into smaller parts. Once clean, keep a really close eye on it - the minute she is finished with one group of toys, make her put it away before she is allowed to start something else. Repetition and consistency are the only way to force the neat habit.

Also, do you have a particularly high standard of "clean"? Reason I ask is that as a kid it was not enough for my mum if my Barbies, for example, were all in my toybox. I had to put the shoes in the "shoe" box, the food in the "food" box and so on. It was really insane when I think back to it. I remember massive fights with my mum when she threatened to throw them all out if they weren't "organised" to her standard. Very few children are naturally so anal about organisation (she has since apologised for being so OTT!)