From left to right, foreground to background.
The design is fine. Biggest problem is the K on the chest piece. Use a letter that has symmetry, like an A, O, U , T or W. It looks better and more centered. Otherwise, put a geometric shape around it. Maybe use the dark blue design for his legs as well. Knee high boots?
The lightning bolt is the wrong color. You'd want something that complements blue, since that's the primary palette. Yellow or white would be fine. If he's supposed to be fast, then have the suit extend over his head as well to imply a streamlined design.
The bricks on the suit are too on the nose. Pure red with darker accents would be fine. Maybe some gloves as well, the arms are over accentuated...
Terrible color combinations. I can't tell what her(?) powers are, but if we're going for green as the focus, then include some yellow to balance it out. The green looks sickly. Maybe also cover her hair, or have it be standing up in a sort of garish look.
Owl boy is basically fine. His face is slightly off, so maybe give him a mask to cover his mouth. In fact, give him a big dumb owl-beak mask and he'd look perfect.