This was a tricky one. Bafflingly, I tried it with all age groups and the same proportion of 4-year-olds as 9-11 year olds got the hang of it. So, I don't know what to tell you. The 7-8 year olds had an inventive field day, complete with lots of engineering planning.
I've also had a lot of success with this activity with older kids in the past, so please do try it with your older students! It's an engineering challenge for the ages.
This Ri Experimental video is an incredibly well-shot and succinct description of the activity, plus it includes a great centre of balance description using a roll of tape.
With the 3-4 year olds, we had to be very aware that this was a high-attention span activity. It was a gamble, and it paid off for about a third of the children, who worked with their parents to make some pretty extraordinary things. The rest just enjoyed building things and yelling "Victoria, Victoria, come see!!!!!!!"
With the kindergarteners, I led the class with a balancing challenge. We stood on one leg with eyes open or closed, on tippy toes or flat feet, with arms out or beside ourselves. This gave the kids a sort of grounding in what we'd be doing without directly introducing the concept of centre of mass. Everyone figured it out.
The 7-8s understood the activity, talked about how heavy things were, and built amazingly complex, lovely silly structures.
And the the 9+ kids didn't get it. At all. Although I have the sneaking suspicion that a fear of failure was holding everyone back, as the younger kids generally figured out by several failed iterations and the oldest were both resistant to advice and unhappy with their less-than-perfect results. Well.
[Best_Wordpress_Gallery id="1" gal_title="Balancing Sculptures"]