Hi Franniemae,
What a wonderful honor to make such a special quilt. She must also like quilts and your sewing to ask you to make such a family treasure.
I would look at the clothing to see what the smallest and biggest size of square or block etc that is possible to get from the clothing. If a clothing piece has special markings then you would want to fussy cut (capture that design centered in the square/block/circle) that piece of clothing. You may want to fussy cut and applique to another larger fabric block.
I would ask her DIL what size of quilt she would desire. That may give you a place to start, the final size. Then go from there. You may need to add additional fabric to the quilt. Does she have a color scheme she would want for the quilt?
I would draw my ideas on a piece of paper. Measure each area possible, twice, before cutting then number it. Then sketch your plan with the numbered areas including their measurements on your plan. You can then decide that you may want to have sashing between the blocks. Then you can decide what size the sashing needs to be, then decide about your borders. I would also overcut by a 1/2 inch to allow for each room and squaring up of each piece.
You might be able to include the front portion of one of his shirts and the bottoms from his pj's. Is there a favorite of each that his mom likes, or one that he always wanted to wear? Are there any special stories or events attached to any outfit?
Is there a special shape or color that either of them like? What does Daddy like? Is there a special piece of clothing from Mom and Dad that she would like to include as well? What about adding in some socks and other small fabric items?
Do you have the EQ program. This is a great tool to use. There is also another program that can be used that's been commented here on the QB, but I can't remember the name of it as I'm writing this. Maybe someone else can comment about some other programs similar to EQ that could be of help. They are not necessary though, they just make the calculations a bit easier. It can be done with paper and pencil and a calculator. I
Does the DIL want to have some input into the outcome of the quilt? Does she want to help design the layout? Does she want to hang it on the wall? Include a hanging sleeve on the back. Don't forget to make a label for the quilt. Does the little one have a special toy? Cars, trains, etc. You could use different pieces from the clothing to make these shapes and include somewhere on the quilt.
Include a very small label about quilt care and washing. A nice addition is to include a pillowcase to store the quilt. This can be made using all the scraps from making the quilt. You then know what is inside as it is stored on the shelf. I would include the pillowcase even if she plans on hanging the quilt on the wall as at some point the quilt will come down. I would include snaps to attach the pillowcase to the back of the quilt when it's hanging on the wall as a place to keep the pillowcase. You could include the special quilt cleaner to go with the quilt.
I hope this makes sense. I hope some of these thoughts help as you work on this wonderful quilt project.
Don't forget to add in allowance for the seams as you work up your design layout!
Pam M