She might not be lying from her perspective. It could be that she's stuck in her own memories, and what she perceives to be her children--the newcomers to this realm--are actually what she would see to be a ten year old child. She has no reason to question this because of the fact nothing seems out of place to her.

[A little freaky, to be honest! But Newt's comment causes Egon to pause and peer down at her.]

How old are you, anyways?