Adapted from a recent online discussion.

Question: My ex remarried and had a child, now 5; we don't live in the same town. My ex and I are parents of a twentysomething.

I just learned that Ex and the new spouse have never told the 5-year-old that I exist; the child thinks the parents are the only set.

Shouldn't a 5-year-old know something by now? I know it's not my child's place to have said anything, especially when specifically told not to do so, but why does this hurt my feelings so much?

Answer: You've been erased. Of course that hurts.

But it doesn't sound personal at all; it's just cowardly. It's hard to explain adult complexities to kids, so these parents punted.

It'll cost them more the longer they prop up this lie. Their child will find out, obviously, and have the eureka moment: "They lied to me about this, so how can I believe anything they say?" The lie will also damage the relationship between the siblings.

Again, it's not a personal issue for you, since this is their family to mess up. And I firmly believe their choice says nothing about your character, but speaks harshly of theirs.

I also strongly disagree that it wasn't your child's place to say anything. The high road, when "specifically told" to stay quiet, was this: "I refuse to deceive a child for you. I won't offer any information, but also won't lie when asked."

Question: Are you just supposed to randomly mention that the older sibling has a third parent? I wouldn't know how to start that conversation with a 5-year-old. I have an almost-4-year-old myself, and while I know a year is a long time in terms of development, I really don't think she'd get it. She doesn't even grasp that she has four grandparents, because one died before she was born. Even when we try to talk about him, she doesn't grasp that he's her grandpa.

This seems like something best covered when the child gets older and asks questions rather than throwing it at them unprovoked.

Answer: Don't "start a conversation," just mention the fact of it. "Sheila's your mom, but mine - my mother lives in Phoenix." Just facts, no puff or embellishment. Understanding is for later. A child who wants an explanation will ask.

Once the fact is out, then you let the child grow into awareness in age-appropriate ways. Usually that occurs through the child's questions as she/he matures. Answer each query with the fact requested. Again, children who want longer answers will ask follow-up questions.

E-mail Carolyn at tellme@washpost.com.