OK so we made the journey over to Kuta which was around 30min from Nusa Dua. The young fella had a lesson and got straight up in the knee-high reforms on a soft top. Conditions were very easy for kids starting out but it was bloody crowded!
Walking along the beach in Nusa Dua during the week we discovered that there are at least a couple of places with a decent range of surf boards to hire, but they are fairly casual affairs with no websites or formal bookings. The best seems to be "Black Rock", which also offers lessons and is tucked into the "Beach Club at Courtyard by Marriott", next to Grand Hyatt.
There is an easy wave right out front and we have had some fun there for the last few days. This spot doesn't involve a long paddle unlike a lot of the spots at Nusa Dua.
I have been eyeing off a nice looking right out the front of Club Med which works on a lower tide so we may give that a crack today.
Hopefully this is helpful for anyone else with kids heading to Nusa Dua over the holidays.