Principle is simple - a selection of new and interesting bits and pieces in a special box for each child which are brought out for limited periods, maybe when quiet times are needed or they are needing distraction or just for the fun of it.
I've been collecting bits for a while and got round to putting them together today.
So, each one is packed with a few different activities. For Matilda, things like small activity books, block paints, stickers, beads, puzzles etc. For Isaac, sorting games, pipe cleaners, toilet rolls to put things in and draw on, calculator, pegs, stickers etc. I have also got some bigger bits - a cookie tray with magnetic letters, Hama beads for Matilda, rolls of paper etc. which are brought out to complement all that. We still have the toy baskets in the lounge for everyday play and books etc. available all the time.
I know that we will refine and change them as we go - I also know that things like the block paint mit be a mistake but a 6 and a half, I am sure Matilda can use them sensibly. It's more about things which don't require a lot of set up and will occupy them for a good 30 minutes, maybe when I'm cooking dinner or bathing one or the other.
Loads of ideas on Pinterest for these things - check out my board 'Kids Time', search for Busy Bags or Boxes or Quiet Time boxes or Sensory Tubs for other ideas.