It seems like the little Blue Tits have hatched. Probably around May 1st, because around this date the two adults started bringing lots of protein food to the nest: little green caterpillars, spiders and other insects. Too bad I don’t know how many nestlings there are.
A wasp was looking into the hole of the bird house but flew away again – none of the adults were around to take it for another protein meal.
We discovered that the Blue Tits bring insect one by on, in contrast to the House Sparrow who takes a mouth full before returning to the nest: