You want online sharing (use a modern PC instead), need video/micro:bit extensions, or your Win7 lacks SP1/WebView2.
After installing, go to Edit → Settings and reduce "Turbo mode" off by default. Increase the "drag tolerance" for better mouse response on older touchpads. scratch download windows 7
You are teaching a child coding offline, have a stable Win7 SP1 machine, and don't need camera sensing. You want online sharing (use a modern PC