I've left Don Jr. and Eric out of this because neither of them have official positions in the White House, but given how they've inserted themselves heavily into politics, going on television to speak on behalf of the administration, earning lecture fees to talk about the administration and involving themselves in potential political conspiracy with Russians -- and they are hardly toddlers themselves, but 40 and 34-year-old-men respectively, ostensibly running the Trump company while their dad has "recused" himself -- then they're fair game, as well.
Personal, private matters of the family are off-limits. Actual young kids are off-limits. But when you are adults who are actively acting as part of the administration and involving yourselves in criminal espionage...you are not longer "off-limits".