For the celery sticks, try cutting them in pieces a little bigger than your index finger, then fill them with pimento cheese. My mom used to make this for mAy brother and I when we were younger, I loved it! Also, fig newtons are a good snack, or have the kids drink V8splash juice. Lots of fruit and vegetables, it's probably better for them to start liking veggies at an early age.
For a treat, grilled cheese sandwich is fun for the kids(if not very healthy...)
Also, for breakfast, sometimes try making Mickey mouse pancakes with pancake mix. My mom would make one big one and two small cakes for us. She used to arrange the 2 small pancakes at the top and make it look like Mickey Mouse(hence Mickey mouse pancakes:)).
Have fun!