Have you thought much about cornflower?
Don't worry not sure that many people have!
Kids will be fascinated though when they discover Cornflour has bizarre properties!
BEFORE YOU START:- Do this somewhere you don't mind a little bit of mess or lay some newspaper down! Thought I'd just warn you
Mix a regular sized packet of cornflour with 200 ml of ordinary tap water in a big bowl. Don't be disheartened by the fact it doesn't seem to mix very well and really give it some welly...
Play!
The Cornflour/ water mixture makes whats known as a 'Non Newtonian Fluid'. You can punch it (yes really go for it in the punch department) and it feels solid!! yet your fingers can sink into it?
Pick a mound of it up and quickly roll it into a ball like you would plasticine and then let it go! Your lovely solid ball just suddenly disintegrates and becomes a runny goooo!
Good luck!
Amy