Relevant quote - emphasis mine:
"Primary lactase deficiency is genetic, only affects adults and is caused by the absence of a lactase persistence allele.[9][10] It is the most common cause of lactose intolerance as a majority of the world's population lacks these alleles.[11]"
edit: Also, I can't believe you linked to some forum called "The Straight Dope" as your citation.
Did you even bother to follow the link? Here, I extracted the reference for you [1].
"Chinese and Japanese populations typically lose between 80 and 90 percent of their ability to digest lactose within three to four years of weaning." (Swagerty et al, 2002)
Ergo, lactose intolerance is a factor in children in some genetic groups. Your citation (sourced from the same wikipedia page) does not refute that.
According to this indirect citation [1], lactose intolerance varies by age and race, eg 85% of Chinese are lactose intolerant by age 10.
If a significant percentage of a genetic group develops lactose intolerance by age 10, then yes - it would most definitely affect growth.
[1] http://boards.straightdope.com/sdmb/showthread.php?t=485313