Toddlers are often unsteady on their feet and they can easily slip and fall into sharp corners. The raised hearth of the fireplace needs to be padded for their protection. This is a temporary fix and the cushion can be removed easily once your child is past the trip-and-fall stage.
Measure the top of the raised fireplace hearth. Add 2 inches to the length for corner diagonal mitring and side seams. Decide how wide you want the pad to be when it is wrapped around the hearth. It is not necessary to extend the top more than about 4 inches in from the edge. Include the top wrap, depth of the slab and bottom of the slab. This is the width of the material. Add an extra inch for the seams.
The cushion material will be cut in separate pieces that include the top two sides and middle, bottom two sides and middle and the long strip that will cover the edge of the hearth. The top and bottom sections are cut on the diagonal at the corner seams leaving half an inch extra all around to accommodate the seams. This step will ensure that the material fits neatly on both corners.
Stitch the diagonal seams on both the top and bottom. Pin the centre strip, right sides together, to the top piece and stitch all around. Repeat with the bottom section. Stitch the side seams and back seam, but leave a section of the centre open so that the foam pads can be inserted.
Cut the foam padding to fit the inside of the cover. Make it wide enough to wrap over the front of the hearth section. Insert them and hand-stitch the seam shut.
Attach the pad to the raised fireplace hearth by applying Rip Tie Velcro to the top and bottom of the hearth and to the material covered pad. Once the Velcro strips are attached, the pad will be secure and will cushion the edges.
When your child is through the stage where padding is necessary, take up the cushion and Rip Tie Velcro strips. Use Googone to remove any trace of adhesive.
If you wish to fireproof the material, check out reference #4. In general, fireplace slabs are sufficiently wide enough to be cool at the edge, but this precaution may be worth considering.