First of all, you did a lovely job following the prompt. You did a good job of using simple figures that we can easily identify as a father and a child's feet.
Now I feel a little embarassed, because Im the kind of person who constantly reccomends doing cleaner lines, but this is one of the situations that I reccomend the opposite. Its clear you are a bit of a beginner and you took a long time making sure every mark was correct, but that left very little time to add details. I actually have no idea what the two columns in the upper right are for. Your lines are very straight, and that reduces the energy in the figures.
Typically, with big pieces like this, artist's will sketch out the whole scene quickly and roughly, then afterwards, refine the image with darker lines, using darker lead, a pen, ink, and/or liberal use of an eraser.
That process involves a lot more learning than I can give an a critique. What I can do though is reccomend the use of thumbnails the next time you make a piece. A thumbnail is a mini practice doodle of what your final piece is going to be. It can be as big as a postage stamp or a playing card. With it you practice a very rough draft what you plan on drawing and practice the proportions, the shading, the placement of figures of your piece. You draw a thumbnail quickly, and you draw several of them, then you pick the one that you feel works the best.
In those thumbnails, you could have quickly tested if you wanted the slide bigger and covering more of the image, or made the father stand like a giant in front of the kid, or practice how much of the kids' body you wanted to see. If you had drawn a thumbnail of your piece before you drew it, you would have noticed how much white space you had in the image and might have had more time to think of something to put inside of them.
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