That is actually called the cere. It is just above the beak. In certain variations, the cere remains pink on males. I am thinking that Sunny is a hen but Stewie is a male after looking longer at the pics.

Pink ceres doesnt mean hens, it just means cocks. Hens have a whitish with blue tinge cere when they are immature and then it turns brown as they age. Males have pink/purple ceres as babies and then it turns blue as they age with exception of the variations such as Recessive Pied and Danish budgies I hope this makes sense