Avoiding possible redundancy in referring to the age range of individuals

"What do children aged/ages 5 to 11 years old know about the sun?"

I truly believe there is something a tad... non-normative about constructions like "children ages 5 to 11 years old" or "children aged 5 to 11 years old". Isn't that redundant? Shouldn't it read "children aged/ages 5 to 11"?

Solution 1:

Re: "children aged 5 years to 11 years"

I had a professor criticize this construction on the grounds that children are not cheese.

Solution 2:

There is nothing wrong with the phrase "children aged 5 to 11 years old" and it could be used in formal writing without fear of criticism.

One could argue that "children aged 5 to 11" is grammatically incorrect, or at least ambiguous, as it raises the question "5 to 11 what?". From context we know that it is almost certainly years, but it could be months, weeks, days, minutes or any other unit of time.