I wasn't involved much in my nieces lives growing up. We lived in different cities then different countries. I'm not a big fan of kids either. My family seemed sad about it but didn't give me a hard time. They understood I need to do my own thing. Still, I definitely felt guilt for being absent as they grew up. The rest of the family was close.

As they grew older into teenagers I found them more interesting and easier to talk to. They don't seem to care about my not being around when they were younger, they had a good life with good decent parents. And technology has allowed us to catch up and get to know one another. They know (I hope) that I'm around if they have a crisis they can't tell their parents about (an uncle/grandfathers ultimate job)

You're unlikely to convince them and it's not a good idea to say you hate kids in general. Just let them know your available if shit goes down and your needed. In the meanwhile you need to live your life too.