Not only the children but some adults too often appear ill at ease when facing Mary. Maybe it's just that she seemed closed off.
Maybe it's because Mary's body language or demeanor projects Regal Aloofness in spades. It's more "Bow to Me and Fear Me" and a forceful one at that, which makes people recoil. Either she's always like this, or she has cultivated this image of an aloof royal to cover her common roots (an idea that royals are aloof and distant, Royal We and everything). This is often a case when someone wants to Out Royal a Royal.
I always thought that Mary wants to project an image to the world. Strong Earth Mother, maybe she wants to look serene, but looks stern instead. You know, they way one aims to be "benevolent teacher" and ended up being "headmistress from hell".
I mean, it can't just be because her face is scary, Q. Silvia sorry to say that her current face is scary to me but her body language is open, although she looks quite distant at times.
Victoria has a very welcomeful smile and I think she like Leti really has that "let the children come to me" vibe. Madeleine also, especially now she is a mother and not so tanned/orange, she looks like some fairytale princess that draws children in.
Speaking of aloofness, I think Mathilde sometimes gives off this air also, she seems like one of those quiet person whom can be mistaken for snobbery, but her body language is also very open.
Even the epitome of "Royal Aloofness"--more like protocol-enforced aloofness--like QEII and the Japanese Imperial Family has an openness about them.