I would never ask the parents of a missing child to speak if they are not ready to. JMO
I don't think anything is "normal" or "usual" when a child is missing.
We went through months of discussion in the Somer Thompson case about how the mom did not act right. She was bashed and blamed and made fun of from everything from how she cried, lack of tears, how she sang at the vigils, what she wore to the funeral...it went on and on. Look how that turned out. The poor woman had NOTHING to do with Somer's murder. So, a lesson could be learned from that. IMO
I can state several cases where the parents were bashed and blamed for months and had NOTHING to do with it. So, I try not to do that unless there is pretty good reason given by LE.