I only have one kid but I wrk full time, so from when he was born until we moved and I had my sewing room I wasn't able to sew. then I would sew for a few minutes and felt like you I was lacking motivation. I think it is not motivation, you are probably tired. I would not push myself and would wait until the mojo comes back. Maybe what you can do is E-quilt, as I say it, go online, look for patterns and possible projects. Buy yourself a notebook and start a project, think of colors, patterns and measurements. Maybe if you have a stash, start building a kit for a quilt, cut one fabric at the time. Make sure you label everything so you dont forget. If you still dont feel like seating down. Choose another one.
Good luck. Also,while e-quilting (virtual cyber quilting) navegate through patchwork blogs, you will find very different interesting ideas out there. You will see.
Andrea