(it almost seems off-topic to be posting an actual tip but here goes)
top tip:
ask a newsagent for the freebies from unsold childrens magazines - most give them away or will sell them at a small price. Produce these at intervals during the flight. Children love new things, miniture things and breaking things, these fit all the requirements. I got mini playdough kits, small colouring books, little puzzles etc before and the DS's loved them.
very important footnote: get rid of the whistles/trumpets first.
hnok hnok