google 'algebra' or pre-algebra games , there are some really good games available.
i find using a diagram useful when explaining those age questions, bit like a time line.
. put ian in the middle, jump 4 years and put 16,
ian is on 12, so his sister is 6, in 4 years time she will be 10.
for the type where ' in 4 years time Ian will be 'x', use same technique..try actual numbers first , teh child can usually see it straight a way, and then use x to represent a 'mystery number'
algebra at this level is not particularly scary if you point out that they have been doing calculations like this since infants.
3 + [] = 5
[] + 10 = 11
as they get more confident this is a good game
http://www.bbc.co.uk/education/mathsfil ... ostie.html