Super fun concept (I love steampunk-y dirigibles, I have one in my portfolio too ;-) and it looks like you already have some great feedback. These forums are a great place for getting critiques, and its especially awesome when one of the instructors drops in ;-) lucky you! My only comment is your linework seems a little big inconsistent to me--its definitely all there on your dirigible and the dad and the house, but in places like the backpack and the bushes it looks more rendered. Variation in line work can be OK as long as there is some consistency and rhyme and reason to why things are different, which I'm not seeing in the way you have it right now.
You're right @gimmehummus , I tried to make it seem as if the fox is almost about to climb the table, but I didn't draw the body corresponding to its action.
And @Chip.Valecek , can't believe I actually forgot the candle. I got focused on characters too much, and I do remember having a sketch of cake with a candle, but somewhere along the way I forgot completely about it.
I would suggest correcting the gesture on the ninja turtle who is running. Typically, a bipedal running figure has alternating limbs. With his right leg swinging forward, it should be the left arm that is matching it, rather than the limb on the same side.
That said, I really like the gestures of the two middle turtles. The one in the front and the back, I would rework. I also like the stark contrast of the street lamp clearly illuminating just that particular section of the street. That clean line of demarcation from light to dark appeals to me. Very comic book style. I would not recommend changing that, as others have suggested.
Hi Ben! Since others have mentioned color and mediums, I thought I might mention the pose. Right now the character is very off balanced, do to her stance, and the fact that her feet don't seem to be on the same plane. People normally stand with their weight shifted to one leg, which your character seems to be doing, but her leg is too far out to support her. Also, the above shoulder tends to come down towards the raised (weight bearing) hip in order to counter balance, but hers is going away from the hip instead. Since that sounds way too complicated written out I did a quick paintover to explain what I mean. Hope that helps!