How do I set a restriction for apps downloads on my son's iPad?

1. Open the Settings app, then click Screen Time as shown below.

2. Select 'Content and Privacy Restrictions' as shown. You may need to set up Screen Time first if you haven't yet.

3. Turn on the toggle, then click 'iTunes & App Store Purchases'.

4. Now, change the 'Require Password' switch to 'Always Require'.

Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support

GreenDaMan2024 wrote:

Also, Is it possible that I can set a screen time limit on an iPad 4th gen as well?

Oh, I see. Unfortunately, it's not possible to use the built-in Screen Time app, as the iPad 4th gen is limited to iPadOS 10.3.3.

You may have luck searching the App Store for compatible screen-limiting apps.