Do the same as Jack the Reaper: one piece at time. A routine to display the numbers, another to do atithmetics with them, another to the keyboard and so on... them start joining them.

Can you be more specific about the working of that game? Is it a calculator, the random numbers appears to be summed? multiplied?

I don't think that you need external RAM to generate the random numbers. You can generate them "on the fly" or you can have a table with numbers that can be displayed in a random way.

Do you have routines to display charachters in the display? If not lok at the code library, there is a collection of LCD routines there.

Two lines in the display? the first line you can have the first number, the second line the second number and the operation between them. If the child press the correct answer in the keyboard there is a sound from the speaker... is this?