l have 100 is of feet of used climbing rope and wanna make a scramble net for my kids to climb on.What type of knot(s) should be used. How to make each square the same size?

The ones l have seen use other attachments at the joints. You might try marking it with a sharpie to get things the same size. Otherwise, get something square to put in each hole as you go to check if it is the same size.
Here is a small scale example. It might scale up well:
http://cheepparrottoysntips.com/knots.html

Please post your final solution somewhere. l would like to try it.

Google animated knots by grog.

The main rope just forms rows of zig zags - the bottom of each bend attaches to previous row, the top of each bend attaches to the next row. Along the edges there is a straight piece of rope for the border. These r typically tied with a separate type of thinner rope which ''lashes'' the bend from each row together - the commercial ones use a metal connector the crimps the rope together.

If tying this with lashing rope, lay out the large rope with the bends marked out on each strand (which will all be the same length if ur final net is going to be square). Then use some 4 or 5mm accessory cord to lash the marked points together - the double fisherman knot tied over the two main pieces of rope will work.

Good Luck