Some good nicknames for uncles are.
Uncle Bear.
Uncle Hawk.
Uncle Bug.
Uncle Tiger.
Uncle Moose.
Uncle Duckie.
Uncle can be shortened to just plain Unk (i.e. Unk Aidan) or Unks.
There's the Spanish Tio, but it's Oncle in French, and Onkel in German—so there's not a lot of variety there.
Some good nicknames for aunts include.
Zia (Aunt in Italian)
Tia (Spanish)
Tante (French)
Theida (Greek)
Täti- (Finnish)
Tetka- (Croatian)
Aintin (Irish)
Moster (Swedish)
Other great nicknames for aunts include.
Nanny.
Mimi (for aunts with first letter M)
Bubbles.
Cookie.
Bubby.
Tinkerbell.
Tootsie.
Nana.
Some ways to be a good aunt are.
Be the aunt or uncle you wish you had.
Play your niece or nephew's favorite games with them.
Take a walk down memory lane.
Focus on experiences, not gifts.
Act like a kid, plain and simple.
Remember that quality time + unconditional love = a winning combo.