Hi, I have a 3-level house and on the middle level I am getting hairline cracks in the ceiling just in the kitchen and was wondering what the easiest way to fix them myself would be. It is a drywall ceiling and we just moved into the house. It is only 7 years old and I have no clue whether this is normal or if it shows a larger problem. Thanks!!

Yes it is normal and most crack will appear in the first few years of the house beening built, you notice most cracks above door ways and widows, and occasionally on ceilngs , but not as much as the other to.
As far as a fix, its drywall much, you'll need to tap the crack with sheetrock tape, or use the mesh tape, which I use for things like that. Apply the tap and use a 3 or 4 taping knife to apply drywall much, smooth this out, this donest have to be perfect so don't dry,
After this let it dry a day and put another coat on this time using a 6 or 8" knife, make it a little more smoother than the last coat. let this dry, and finally use a 10 or 12" knife for the final coat, this needs to really smooth so it easy to sand after it drys,

Once its dry and you've sanded it, prime it with a good primer, let dry and paint

OR:
You can cut a recessed V notch in the drywall(take your utility knife and cut at an angle,roughly 45% on either side of the entire crack),and use a lightweight spackle compound,commonly found at the paint section in most stores.

Sanding/clean-up are a minimum and painting is not as in depth as finished compound.