'soft spot' definitions:

Definition of 'soft spot'

From: WordNet
noun
A place of especial vulnerability [syn: weak part, weak spot, soft spot] [ant: good part]
noun
A sentimental affection; "she had a soft spot for her youngest son"
noun
Any membranous gap between the bones of the cranium in an infant or fetus [syn: fontanelle, fontanel, soft spot]