Extensive snorkeling and freediving experience at this point IMO would be the best thing. There is no substitute for the skills learned from skindiving, comfort in the water, learning to use fins naturally, mask clearing, breath hold, ear clearing, etc.
Starting immediately into scuba leads to a life of dependence on mechanical devices and conditions a reliance on gear and the specific skewed techniques associated with using that modern gear (including elevator diving, body positioning, and some very specific finning techniques), rather that learning the core basics of watermanship without all that scuba centric stuff first, then once true watermanship is learned then adding scuba later onto a firmly grounded core. The final attitude, outlook, and skill level are two completely different things from one training methodology to the other.
Unfortunately through the years, proficiency in skin diving/freediving/snorkeling has been eliminated in favor of a conveyor belt training system in the modern scuba training world to run as many people through in the shortest amount of time possible.
You have a chance to set them on the right track now which will cement their love of the ocean forever through confidence and skill, instead of possibly turning it into a casual curiosity that will soon be abandoned.