If you've had a go at all the ones above, here are some more ideas to try...
problem
Favourite
Counting Cards
Age
7 to 11
Challenge level
A magician took a suit of thirteen cards and held them in his hand
face down. Every card he revealed had the same value as the one he
had just finished spelling. How did this work?
problem
Favourite
Up and Down Staircases
Age
7 to 11
Challenge level
One block is needed to make an up-and-down staircase, with one step up and one step down. How many blocks would be needed to build an up-and-down staircase with 5 steps up and 5 steps down?
problem
Favourite
Sitting round the party tables
Age
5 to 11
Challenge level
Sweets are given out to party-goers in a particular way. Investigate the total number of sweets received by people sitting in different positions.
problem
Tea Cups
Age
7 to 14
Challenge level
Place the 16 different combinations of cup/saucer in this 4 by 4 arrangement so that no row or column contains more than one cup or saucer of the same colour.
problem
Favourite
How Tall?
Age
5 to 11
Challenge level
A group of children are discussing the height of a tall tree. How would you go about finding out its height?