No. They will not become more aggressive or bitey. The ferrets are smart and can distinguish food from humans. Mine see their live prey as a treat and get really excited. At the end of the day, my fuzzies still cuddle and give me kisses.
Ferrets, or any animal, should be supervised with any child anyway. Ferrets play rough, so your dad's gf needs to know the difference between aggressive biting and play biting. Ferrets who bite aggressively clamp down and do not let go. If they're already pretty calm or play nice with people, I wouldn't worry about an increase in aggression unless they have Adrenal disease, which does increase aggression.
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