My three little nephews are adorable and are always well behaved when Uncle Clemenza is around. I can tolerate (and even enjoy) children in small doses.
I'm glad you have a good relationship with your nephews... I'm sure they appreciate it, and will appreciate it more as they get older. It can be fun for you, too. If I didn't have kids (I tried for 10 years before having my daughter), I planned to be "Crazy Old Aunt Penny" with 12 cats and 15 pomeranians.
Ah, the best laid plans...