welcome in H.C.M.
I have gone through your query regarding some soft tissue
lump you have noticed inside the throat of your grand daughter who is three years old only.
As you said that your grand daughter is asymptomatic, so I am suspecting these possibilities-
(1) Enlarge and hypertrophied lymphoid follicles of base of tongue
(2) It may be Epiglottis
you might have seen.
(3) Much enlarge Adenoids
(4) Part of anterochoanal polyp.
In this list of four first two are are physiological and needs no treatment, but last two are to be managed by expert hands of E.N.T.specialist.
So to conclude the matter thorough examination is must therefore try to consult your E.N.T.specialist.
Hope you got the clarification of your query