Tsk. [ He clicks his tongue. ] What generosity? You are a child. It is my responsibility as an adult to look after you when your guardian is absent.

[ This is just one of the many responsibilities of an adult. Not a big deal at all. ]

'Bull' is the proper term used on Earth and other worlds I know of. 'Shit' is crude slang for feces.

'Bullshit' is mostly used to call out something for being complete nonsense, or a lie while 'shit' is more of a general expletive that can be used in many ways.

As an example, when something goes wrong or something bad happens I will say or think 'shit'. Using expletives can help calm you down in stressful situations and even make pain more tolerable.

[ He pauses. ]

...But since you're still a child you shouldn't use expletives. Try using 'crap' instead of 'shit'.