I spent the 10 hours flight LA-Munich mainly standing up, walking or sitting on the armrest while the two kids occupied three chairs sleeping, which was totally fine, who wants to sit for 10 hours with cranky underslept kids. Then spent two hours with the noisiest kids on the Munich airport and two more on the Munich-Sofia plane. The little one said "Daddy, we going into the plane's belly" and yeah, that's exactly how I felt at the end of the journey: as something that has been into someone's belly and then followed its natural way back to the light of day.
The important thing is that we're here now and the joy of getting together grandparents and grandchildren: priceless. Other than that Bulgaria is cool, unseasonably.