Many girls are prone to labial fusion or adhesion.  This is when the inner "lips" of the vagina seal shut.  This only happens in girls who have not yet reached puberty, and it always goes away (un-seals) spontaneously when they reach puberty due to the effects of estrogen on the vaginal mucous membranes.

In boys, it is the foreskin that gets stuck to the glans (head) of the penis.  This is true most often in uncircumcised boys, since they have more foreskin to begin with and it's normally "glued" to the glans at birth... only gradually separating over the first several years of life.  (It's a myth that the foreskin should be fully retractible - this is rarely true until after puberty.)  When boys are circumcised, the first thing the surgeon does is to "unstick" the foreskin from the glans.  Sometimes afterwards, however, the remains of the foreskin re-seal - and the foreskin even in circumcised boys may not retract fully.  This area of adhesion can, moreover, become the site of smegma collections - white lumps of cheezey material building up between the foreskin and the glans - which can be unsightly but which are harmless and go away by themselves as the boy gets older and the adhesions naturally dissolve.

Both foreskin adhesions in boys and labial adhesions in girls are something many doctors unnecessarily feel compelled to manually tear open, causing needless pain.   Most often they just seal up again anyway.  So long as the adhesions are incomplete - meaning there is still enough of an opening to allow free flow of urine when voiding, they cause no harm and treatment of any sort is unnecessary.  They will open up by themselves at puberty, if not before, through natural mechanical effects and/or the effects of sex hormones (estrogen or testosterone) that appear at puberty.

Younger doctors more often will use estrogen cream for labial adhesions in girls.  This has proven safe and effective in the SHORT RUN (i.e. the next few years).  I worry about possible effects 20 or 30 years down the road, however, which of course hasn't been studied.  There is no equivalent treatment for boys.

Our opinion is it's best to do nothing with these things.  Time and maturing will open them up on it's own, and it isn't really harming the child (except, in a rare instance when things are closed up so tight that it obstructs urine flow, in which case treatment is justified.  IF treatment is either desired or necessary due to urinary obstruction, then estrogen cream is the treatment of choice for girls, and circumcision (under anesthesia) is the treatment for boys - alternatives of manually pulling them apart then using things like Vaseline is not only painful but has a high relapse rate (they just seal up again).