What piano tutor do your children use?
DS2 started with Me and My Piano 1&2 (Fanny Waterman - Faber), which was superb: great, fun pieces - he loved it and made rapid progress.
Unfortunately Faber don't do a sequel to this series. So then he moved on to OUP's Piano Time 2, and I have to say I loathe it! The pieces are quite tricky, but also fairly boring, and very 'exercise-like'.
(He does have "Dozen a Day", which he loves; and also "UpGrade" - repertoire pieces, which he plays just for fun. And his teacher has just asked us to get the AB Grade 1 pieces - so he has plenty to work on. But I just wondered what good tutor books there are out there for this stage?)