|I made a jacket/pants set for my granddaughter for Christmas and used this trick I also use for applique: pockets and flaps (this had cargo pockets) could be a nightmare because fleece has so much give. I cut out the pockets and flaps of fleece with matching linings of fusible interfacing (lightweight) and sewed them with the right side of the fleece and the fusible side of the interfacing together, completely around. Then I cut a large slit into the fusible interfacing and turned it inside out, fused it. The fusing will reclose your slit and give you neat finished edges on all sides of the fleece (pocket, flap, whatever), so all you need do is top stitch it onto the garment. I put the slit in the direction where it was less likely to be rubbed repeatedly (up and down on a pocket as opposed to across the width) because the fusible "quits" eventually, as we all know. It stabilizes the pocket against stretch and gives you bottom stabilizing for any embellishment (I embroidered on the pocket).
For applique it can be done with the fusible part facing either way, depending on which fabric you think needs more stabilizing. Sometimes you want to fuse the applique design onto the fabric and so you put right side of fabric to unfused side of interfacing, and still sew all the way around and cut a slit, then turn inside out and fuse the applique in place. No one will be seeing your slit, you will have clean edges and again can just top stitch.