simplest course is to excavate the lower part where it starts to rise up, get an area level there - you'd then need to have a retaining wall put in to keep back the sloped part leading up the patio. You're talking major land works with diggers, and frankly, this is a professional job, and not one I'd attempt without professional help.

I agree with Bamboo that is a considerable slope, would be different if you wanted to terrace part of for flower beds but an area for football and a largish pool needs professionals. You could always suggest the children go to the park to play football and the top of the garden looks flat enough for the pool.

I was going to suggest the park too! We had 4 kids on a very steep hill & I can't tell you the number of balls that got lost - and football in the garden was out of the question. Good for rolling down though - we used to have an area called "the rolly garden" - so there are compensations.

I love it the 'rolly garden'!