hi, have you thought about bracelet making? Alls youll need is some legnths of string or colored ribbon and beads...you could present this activity to the children in individual little bag Coloring - cheep and effective cut individual pages from coloring book and put a few crayons/pens out how about a treasure hunt around the house and the end clue they get a prize each- you can get some good treasure hunt clues from google and can have as many as you want or make it as difficult as you want to prolong the game
When I was that age I used to love making "dreams" (like in the BFG!!) by putting things like water, oil, glitter, shells, coloured bits and pieces etc, in a jam jar and shaking it up. I was easily amused though.
Also, stamping is always fun but maybe potato stamping s not sophisticated enough for the youth of today!
Get some plant trays/ silver foil and then with a base layer of soil get them each to build a mini shelter, you just need a y-shaped stick each, lots of straight sticks and some bracken/moss for leaves to cover them. Twine too around the key sticks if you want the structure to last till they get home. You can get them to add shells/ pebbles for the garden, maybe even make some wooden fence/ furniture. The finished product is about 10-15 cm tall, perfect for passing fairies, you could even get them to make some fairies with a bead, pipecleaners and some wool wrapped around for clothes. Put them outside while you have the tea and you never know some fairies might leave some fairy dust (or your dh might sprinkle some glitter inside each one).