Hi My Nephew Is 9 Years Old. Last Week He

Hi my nephew is 9 years old. Last week he had a little accident playing with his friends and sadly the one who took the hard beat was my nephew. In the grass was a sharp piece of tree trunk that was sticking out. However, the kids were playing and somehow my nephew tripped in the ground. In the moment he falls down, his legs got cut by a sharp piece of the tree trunk. After the cut, his entire skin tissue (around the tibia/fibula) open up really widely and apparently the cut was really deep. The doctors give him 15 stitches inside the skin tissue and 18 stitches outside the skin tissue. My question will be do you believe the skin tissue will be cured quickly or he might have to take therapies to his leg? We are worried that he might not able to use his leg like he used to.