Observed by watching a child's reaction to surrounding sounds

A) heredity
B) failure to thrive (FTT)
C) attachment
D) separate reception area
E) disposable emesis basin
F) neglect
G) abuse
H) gait
I) vaccination information statement (VIS)
J) hearing

The term that matches the definition "Observed by watching a child's reaction to surrounding sounds" is "hearing." This is because hearing is the sense that allows us to perceive sound, and observing a child's reaction to sounds is a direct way to assess their hearing ability.