I found this activity on several blogs- like here and here and I gave it a try. It was a perfect activity for my girls- they loved it! You can do "liquid chalk" very easy by your own- you only need:
cornstarch/ cornflour (1 part)
water (1 part or a bit less)
food colour (mine was crappy and the colours were not very strong)
Then you can start painting, dripping, experimenting outside on the road...
Neomi kept saying how smooth her hands were from the colour and they liked to touch the dried chalk, step on it, scratch it away in the end...
It washes away very easy. That was for sure not the last time we made this and next time I will make a bigger amount to last longer.