If you are using Restrictions (Settings App > Restrictions) to set this up, and have Sfari turned off, and he doesn't have the restrictions passcode, no he will not be able to access Safari. You should also consider turning off the following:
- Installing apps (this will prevent him from downloading additional browsers)
- Deleting Apps (maybe, might not be essential for your purposes)
- In-App purchased (see above)
In lieu of turning off Safari, you might also consider modifying ALLOWED CONTENT settings to prevent unsuitable content from being accessed, but its not clear why you want to do this, so that might not be what you are after.