Hi Lindyloo
Sorry to hear of your son's diagnosis
I would think that if you are being offered a pump you should go for it.
For very small children the pen choices of '1 unit' or 'half a unit' can be hopelessly imprecise. Even as an adult my usual breakfast or lunchtime doses are only 3 or 4 units. When I was on MDI (multiple daily injections via a pen) I only had the option of changing those doses by 25% or 33%. A pump can deliver meal doses in tiny increments (say 0.05u) so you can tailor doses far more accurately.
The 'constant trickle' background dose can be adjusted much more finely too - and can be changed 'on the go' for periods of running around/trips to the park etc which can guard against hypos. This can also come in very hand when background insulin needs start changing with growth spurts and so on. Additionally, because you *always* have your insulin with you impromptu treats/cakes/ice creams etc are more easily managed because there is no chance of having 'left the pen at home'.
Since you have not got much experience of the way things work you won't have to 'unlearn' anything from injections either - and you should get a *lot* of detailed support in the early days/weeks. My DSN called me several times a day at the start.
Many children do very well on pumps. Kids are very adaptable and get used to wearing something 24/7 more easily than some adults I think too. The sticky stuff that holds the cannula in place is pretty secure, and you can tape down some of the tubing with micropore to guard against accidentally yanking it out too.
Some pumps are specified as waterproof, others integrate continuous glucose monitors and can even suspend insulin delivery if levels drop too low. In the next few years we also might be able to get remote monitoring devices which relay pump alerts to parent bedrooms overnight (eg MySentry available in the US for Medtronic pumps)
It will mean quite a lot of work and monitoring in the early days, but I would think that in the medium-long term it would give your son the best chance of great levels and increased flexibility.
Good luck with your decision.