I'm amazed most of all they were able to keep it under wraps with 4 children involved. I don't think you could pay my children at that age $1 million to keep their mouth shut even under the same risks.
That's the reason the first attempt was just the Strelzyks...
The repressive state apparatus was moving too slow. Maybe they hoped there won't be a second attempt after the first one failed, maybe it wasn't promptly reported to the appartchikhs and handled internally by the Stasi to avoid backlash.
Children put in serious situations are capable of much more serious behavior, than children who have only known comfort and safety.