My 3 year old son wore through the knee of his trousers but they still fit very well. I suspect this might the first of many times this happens, so I could took the opportunity to try some creative mending.
I had to open up the outside side seam as I couldn't get the leg onto my sewing machine free arm.
I used bondaweb to attach a large patch of fabric on the inside to strengthen the knee and appliquéd a rocket shape over the worn patch. I used straight stitch to do the flames, the built in stitches on my machine to add some stars and free machine embroidery to add a planet.
The final step was to sew up the side seam again and done!
As both pieces of fabric I used were recycled from old trousers, the project ticked all my boxes - it was environmentally friendly, budget friendly and fun to do.