In a small bowl, mix together 4 TBLspns peanut butter and 1 TBLspn ground flaxseed.
Spread some onto each piece of bread, using it all up.
Add your jelly/berries to two pieces of bread and assemble sandwiches.
Notes
A word on peanut butter & jelly:
Be sure to find options that do not contain hydrogenated oils or high fructose corn syrup. Your kids will enjoy better health without these harmful man-made additives, and it's easy to find substitutes without them. A word on Flaxseed:
I learned recently that grinding your own flaxseed at home (with a simple coffee grinder or the like) is much healthier than buying it pre-ground. The grinding process releases the oils to the oxygen, which then breaks them down over time.
Try to buy the whole flaxseed and grind it up just before using.