AU I have never heard of those blocks...do you have a source link? Sounds a bit like tee shirt transfer material? Kinda plastic-y.
It may be prudent to wash the blocks before quilting?
But honestly, if these blocks are printed on that plastic matrix, are they really ideal for setting in a quilt? I would at least make it a wall quilt, not one washed regularly.
Others must have used children's art as a component of a quilt...what other approaches might work better for a quilt used regularly as a quilt?