thank you for your query.
yes,it is normal for for kids undergoing puberty
to have swellings under nipples.
since you have not mentioned your sex,i'll describe condition in both males and females.
Most breast lumps in men are actually a condition called gynaecomastia
, a button-like growth under the nipple and areola
area that can be felt and is sometimes visible to the naked eye and occasionally it can be quite tender.
This increase in the amount of breast tissue is not a tumour and occurs due to changes in hormone balances at times like adolescence.
In females,The first sign of puberty in a girl is usually breast development. This starts with the appearance of a 'button' of breast tissue behind the nipple,One breast may start to develop weeks or even months before the other one and only later will the breasts start to change shape and enlarge.
hence there can be differences in the pectoral size in both sexes.it genereally evens out in due course.in females the breast bud grows out to form proper breasts.
in males this can be reduced by proper exercises and food.in cases where it doesnt disappear even after completion of puberty gyneacomastia or removal of fatty tissue under nipples in done.
wishing you good health