My kid's were 16, 11 and 9 when we ran for our lives.
I was ill for a while and didn't discuss the situation straight away . . . but when I did I was careful to begin by asking them how they felt about the things they had learned at the KH . . . only that . . . without counter argument.
I was pleasantly suprised that while they asked the occasional question . . . the three of them absolutely HATED the meetings, HATED field service and were really glad they didn't have to do it anymore.
I know your circumstances differ Julia, but it might be relevant in that if you be available simply as a sounding board for them at first, you will get to know what they really think . . . not what they think you want to hear. Then you have a starting place. Additionally . . . they will have little to "quote" you on reducing the possibility of them being in the middle of a debate which could trouble them.
Being a sounding board mostly will provide a place of security for them . . . then you can progressively deal with their fear and guilt which the WT will undoubtedly instill . . . and this will give them relief.
Good question . . . and some good answers here . . . pick the bits that suit your situation