Teaching harmony singing to children?

So here's a question that came in about teaching kids to sing in harmony:

I am involved the our Son-Shine choir ministry of our church, ages 4-10 (young as mature 2 year, maybe a delayed shy 12 year old.) How important is it to teach parts at this ages?

Or when should parts teaching begin?

I grew up listening to choirs, both in church services and in rehearsals (my father was a choir director and my mother sang). I acquired the skill through osmosis. I don't remember how old I was when I learned to harmonize, but I was definitely younger than 10. For kids who were not around choirs all the time, it might take longer.

The youngest choir I've ever directed was teens (the youngest was a 9-year-old who sang very well), and I was able to teach them some harmonizing. But I found an article where some music teachers give their recommendations for what ages are ready for what types of singing. The article suggests that most children are ready for real harmonizing (everyone singing the same lines, but on different notes) at about the age of 10 or 11.

There are two things I have recommended in the past when working with singers who don't have experience singing in parts:

• Start with songs where the different sections are singing completely different lyrics and melodic lines. The singers will find it easier to hold onto their part when it's "independent" of the other parts.

• My other technique is to choose songs where the soprano part is so high that the altos wouldn't be able to switch over to the soprano part. But that might not work with the vocal ranges of children.

The articles that I found that talk about teaching harmonizing to children suggest the same approach, starting with rounds and canons. Here are links to two article that focus on children – Part Singing: A Skill unto Itself and Building Part-Singing Skills in Children's Choirs.