Not sure what flash you are using, nor how the "flash" part of the exposure is being regulated, nor exactly what you mean by "eyes to look like that". Do you mean eyes with big, round dialated pupils??? From the kids being in low light???
Need to know the manner the flash output is being regulated: Manual? AUTO-thyristor mode? e-TTL? e-TTL + Exposure Compensation?
Possibilities include: increasing flash-to-subject distance. Lowering the camera's ISO value while keeping the flash set identically. ELEVATING the ISO value set on the flash, while keeping the camera set identically. Closing the lens aperture down a bit. Dialing in MORE MINUS Exposure Compensation on the flash. Some of these approaches will work in AUTO or TTL modes, others will not work. Again, we need more info on HOW the flash is being controlled!!! Bottom line, the faces need less light on them.