Well, it is true.
"Originally modeled on a spirited kindergarten-aged boy. The smock and satchel were adapted for adventuring. It occurred to me after that if Lalafell were taller, this might resemble a <can't read> in Dragon Quest
<someone with better eyes confirm this last bit?>
As far as using a child to model clothes - Lalafell barely hit 3' as a max height. I'm thinking a kid was probably easier to find vs. a dwarf for sizing purposes. In addition to that, the exert mentions how the outfit was outfitted for adventuring. I've never once thought that the outfits have looked like children's clothes. They fit in just fine with the other racial outfits (several which also include a dress/skirt variety for their females).
I'd say Lalafell fall more into the chibi category as they are definitely cute and tiny and a bit more exaggerated in their shape than the other races. I do think that Lalafell, out of all the races, are definitely the most childlike - but I've never viewed mine or any as an actual child. The game also doesn't view or treat them as children either. As it was mentioned earlier in this thread, there are Lalas doing plenty of horrible things in this game, none of which would be suitable for an actual child to be taking part in.