Thanks I have passed along your suggestions plus sent them a link to the Victoria Model Boat club or VSSS.

Hi Grandpa, further to Dave M, depending on the boats you choose, drill a small hole in the prop shaft, just before the inner bearing, this would allow a spray of WD40 type oil as a cleaner then a couple of drops of lub oil for the bearings. Like Dave said, flush with fresh water, salt water will ruin the prop shafts within days, if its left.
Regards
Mark

Hi Grandpa
I agree with canabus, but toy boats may not have oiler points on the prop tube and to protect the shaft and bearings I suspect you would need to remove the shaft after each sail and run fresh water thro the prop tube to remove all the salt which will otherwise dry and crystalize. The salt crystals will then act similar to sandpaper and ruin the bearings, I know I speak from experience!😭
Once clean let the water drain then lube and spray as suggested.
I do hope the boys are able to enjoy their models
Regards
Dave

Hi
Wash in fresh water with a bit of soap and lube the drive shaft.
WD40 spray around the prop and rudder.
For lube I use plumper silicon grease as it is water proof.