Any trip through the park, by definition means a greater risk of ending up on the "DL" (disabled list). Most resorts have pros who can teach your son how to have fun "saferly" in the terrain park, some won't because of insurance reasons. If a resort school does not have a specific terrain park lesson product, they will often just teach terrain park within their normal lesson product. Just ask.
If you want to proceed teaching your son on your own two good places to start are the NSP Smart Style
guidelines and the PSIA ATML model. Smart Style is pretty cool for educators because it's a starting point for discussion. It does not work as well for the inexperienced to self learn. For example, #4 "Respect gets respect" does not say "Call your drops" or "Don't rag on newbies". But anyone with experience in the park knows that we often have to take turns on features and need to clear out from landing areas promptly is we can. We also know that getting upset at other people who lack respect does not help either. Most parks are busy enough that you can observe good and bad behavior in a short amount of time just watching. #3 "Easy Style It" is a great lynchpin for safer ways to learn. There are lots of techniques for using features in such a way as to make the difficulty factor very adjustible. One example is determining a starting point for approaching a jump by where the lip of the jump is relative to eye level when sitting. For normal snow, starting at a point where your eyes are level with the lip will give you just enough speed to just ride over the jump versus getting air. After doing that for reference, you go bigger by moving your start further up the hill on subsequent jumps. Another example using the sides of jumps at an angle to go "smaller". I've had several adult+child lessons where the adults who were "just watching" found these jumps irresistable. They go over the jumps at a low angle and get a few inches of air while their kids take the jump at a larger angle and get 1-2 feet of air. It does not take much creativity to figure out easier ways of doing things, but some of the tricks for doing so are not intuitively obvious to everyone.
The ATML model stands for Approach, Take Off, Manuever and Landing. Every terrain park feature can be planned for by breaking it down into these four pieces. On approach we want to note if the approach is straight, smooth (no ruts) and level (versus on a double fall line). During approach, we typically want to get low in preparation for take off. We want to plan our approach to generate the speed that we need. Will we be riding straight at the jump or use speed checks? There are many different types of "kickers" for jumps. We want to plan for whether and how much we need to add pop at take off and understand what flight path the kicker is going to send us on. In the air we may simply want to retract the landing gear on take off and then extend in prior to landing for our "manuever" or we may want to add a trick like a grab or a spin. For landing we need to plan where on the landing ramp we intend to land. A safe plan, for example, would target for the middle third of the length of the ramp. There are times when we want to land heels first and there are times we want to land toes first. It all depends on the jump trajectory versus the pitch of the landing ramp.
Safety gear is a topic you'll want to do some research on. Helmets are a must. Parents wearing helmets get a good example. Other safety products like wrist guards, knee pads, hip and back protectors may be overkill for kid getting 6 inches off the ground, especially when they'll need to be replaced every other year for growth. But eventually, hard falls become more of a matter of when versus if. The more experienced one gets, the bigger one tends to go. The bigger one goes, the harder the fall. The harder the fall, the more damage. The more protection, the less damage. So it goes.
One thing that is difficult to teach is how to fall. The general rule is that you're much better off not fighting a fall. It's better to give up than try to "save it". "Tuck and roll" used to be a basic in kids gym classes, but it's not universlly taught. Dry land practice with mats is not a bad idea. Practicing "quiet" landings versus "loud" landings is another great dryland exercise.
To answer some of your questions specifically:
Most of the time you want to extend off the kicker to add height to the jump versus prejump like racers to minimize the height.
For most of your beginner jumps you will want to land tips first to get better absorption of the landing by using some of the ski flex, but you will quickly want to match your landing style to the jump tracjectory. The more vertical your flight path is relative to the landing, the further back you want to land to avoid going head over heels after landing.
Here are some other resources to consider:PSIA park and pipe FAQPSIA Park and Pipe Instructors guideNewschoolers forum
(Way more intense on freestyle than this place)