How about 'everyone's recipe is different, some people's recipes might mean they need extra help, they might need to use a wheelchair/hearing aid/take medicines'
Some recipes mean people have blue eyes, and some that they have brown.
Some recipes mean people have straight hair, some make it curly.
Some recipes make people good at doing somethings easily, such as if you are tall you can get things from high shelves, sometimes the recipe makes it harder to do things, small people find it harder to reach tall shelves.
Ellie Simmonds is a good example of having genes that make it harder to win swimming competitions but that doesn't mean it is impossible.
Sometimes the recipe makes it easy for things that are not very nice to happen, such as making people break bones easily, or makes it easy for them to get ill.
I don't think age 6 need more than this, I think disability awareness is a different topic and I think it is too much to go into detail about genetic and or congenital illnesses. Or genetic predisposition to illnesses.
I've done an equality and diversity presentation comparing people to fruit that could be changed for this.
All fruit is fruit, just like all people are people. But fruit is all different shapes and sizes and the shape, size and taste is because of the tree it was picked from.
Different fruit is better at different things, if you want to draw a yellow fruit then a banana or a mango but not a strawberry.
If you want to eat a fruit with the skin on then an apple is better than an orange.
That sort of thing.