There are some child-freindly 3D apps out there, but 11 is probably old enough to start. The community is very helpfull and there is a ton of good learning mate

There are some child-freindly 3D apps out there, but 11 is probably old enough to start. The community is very helpfull and there is a ton of good learning material. The key thing, as with all apps, will be to demonsnste that 90 % of what they need to learn can be covered with 10% of the UI.