you would need help for this, however, I had the same problem with my tank in the basement. The hose idea works.... right up until you need to do decent water changes. I went to target and got one of those 10gal storage containers. I use that to fill the tank.... I only fill it 5-7 gallons worth, so it takes a few trips still but that is the only amount I can hold without spilling it.
What you could try, in some order or another, put the fish in the container with the original water that the kid has them in now. Then when you get the tank set up, put that water with the fish in the tank. Then from the sink (taking for granted that your tap is pretty clean) fill up the container again, use some water conditioner and put that in... That will give you a little under half your tank probably (its 40 gallons right). After that its up to you how much new water you want to put in at once. You could put a little mroe in then wait a day, or put it all in, but at least then you have some of the original water to mix with.
does that make sense? hope it helps*thumbsups