were you planning on adding borders?
Cutting squares out at 5" gives you a FINISHED size of 13" blocks. You can normally get 8 5" squares out of a WOF. That means for your strip color and your main color, each WOF gives you enough for 2 blocks. For your little square color, each WOF gives you enough for 8 blocks.
A simple 3 x 4 block, no border, layout would be about 39" x 52", which would be a common size that I use for baby quilts. (I don't have a toddler bed to lay this on for comparison.) This means you would need 12 blocks. Since each WOF of the strip & the main square gives you 2 blocks, you need 6 WOF or (5" x 6 WOF = ) 30" - if all cutting is perfect!. Since each WOF of the little squares gives you 8 blocks worth, you need two WOF or (5" x 2 WOF = ) 10" .
I would add at least 1/8 of a yard (probably closer to a 1/4 since each strip you're cutting is 5") to account for any cutting mishaps. So that means 1 1/8 yards of the main two colors and 1/2 yard of the little square.
If you want to add borders to make the quilt bigger or add extra blocks to make the quilt bigger, that will affect your measurements. But know that using 5" squares, each WOF of the main 2 colors will give you 2 blocks and each WOF of the little square color will give you 8 blocks.