My baby is 5 months 1day he is keeping the thumb in is mouth he can keep or not

A. good afternoon j   thumb sucking is naturs way of soothing, comforting, it normally occurs at 3 to 4 mths of age. try involving your baby in other activity to decrease thumb sucking. normally child outgroWS this habit by 3 yrs of age. if it continues beyond that, if it interfers with speech, eating, or other finger activities , consult your paediatrician.