How about quilting diagonally through the squares and cornerstones using a medium gray or blue cotton thread. I've never had much success with invisible thread. Staying in the ditch is also a challkenge for me.

I want to chime in about stitch in the ditch also. For me, it's one of the most difficult ways to quilt with a walking foot! Requires a lot of concentration, and I am never satisfied with my ability to stay in the ditch (or keep an even distance from it). I like the idea of doing diagonals to avoid having to do SITD. Also, you may want to consider a more modern alternative, which is to use a walking foot to make wavy lines through the quilt. This is actually easier than trying to make straight lines as there is no "wrong" way to do it. There are a number of tutorials online, and you can Google "wavy quilting lines" and click on "images" to see some of the possibilities. I will link a few here:
http://sewsweetness.com/2011/09/back...and-other.html
http://bastingbeauty.com/2014/03/25/...wavy-quilting/
http://betteroffthread.com/2013/03/0...ting-tutorial/
https://sewfreshquilts.blogspot.com/...l-habitat.html

I started to ask if FMQing in the ditch might be easier, but I'm not ready to tackle that yet. I'm picking up my 15-91 on Monday, which will be my FMQ machine. However, the best machine in the world will not make up for lack of experience.

I think I will make up some dummy squares and see what works best and is easiest. I'm into doing what will be successful. As I go forward, I'll be able to tackle more difficult techniques. Failure is discouraging, so I don't want to go there.

I have some left over Warm and Natural 80/20 from my last project. Will it be much different from the 100 cotton?

bkay

Bkay,
FMQing in the ditch is usually harder because you need to manage both to stay in the ditch & to keep stitch length consistent.
The 80/20 is noticeably higher loft than W&N (which isn't 100% cotton, but something like 87% cotton & 13% synthetic scrim). It's not an enormous difference, but it is visible. The bonding process is also different, requiring a quilting distance of no more than 5" to preserve the batt (which I would argue is still too far apart for a child's utility quilt).

I'm talking about using my scraps of 80/20 to practice stitch in the ditch with some dummy squares. Will it handle much differently than the cotton? It's just an experiment, and will probably go in the trash when I learn what I need to know. It will not get washed ir used, so that is not an issue. It's just a practice item.

If it will be that different, I probably have enough leftovers from the batting I bought for the I spy quilt to make up a couple of dummies to experiment with. I just wanted it pristine when I got ready to sandwich the quilt.

So, does it handle that differently?

bkay

There won't be a lot of difference. I would go ahead and use the scraps for practice. They will work fine.

As long as you use polyester invisible thread you will be ok. Use regular thread in the bobbin. The newer polyester invisible threads work very well.

I don't know what machine you have, but there is a "stitch-in-the-ditch" foot for my Pfaff. I stitched in the ditch for a wall hanging and found it much harder than I had expected. Then, my quilt shop had me try the new foot. It was like a miracle. The foot has a sort of prow, and it just makes it easy to stay right in the ditch.

I agree with Bree...for a child's quilt, it really should be quilted much closer than 10 inches. I just gifted a Warm Wishes quilt to our new nephew which I simply used my walking foot to do cross hatching about 2 inches apart. You could use light color thread on top and dark blue in your bobbin. I would post a picture but I haven't figured out how to do it from my new Ipad (sigh).

I haven't used the mono-filament thread in quite a while because I have enough trouble threading colored thread. Since you have all these wonderful and bright colors, why not use a variegated thread on the top. I like using variegated thread on a quilt top as it adds another dimension to the quilt. Instead of quilting in the ditch, perhaps you might try quilting with cross-hatching through the blocks, corner to corner, as it will actually take a little less time than in the ditch. I really like your quilt. Thanks for sharing.