I can see everyone's position here, but what is done is done. I suggest you continue to be open to the friendship and consistent that you regret the way your friends feel but you did nothing wrong. If they choose to make a mountain out of a molehill that is their concern.
It is not uncommon for couples who were friends before kids to drift apart after kids. This couple thinks they can be spontaneous and show up anytime. Maybe that was you once upon a time, but not now. Only someone without children would think they could show up at bedtime and command your attention. I do think there is a middle ground where you say "busy now, but available in a half hour", but that's for next time.
On a slightly related topic, you need a better bedtime routine.