Mostly their childhood lasted 50 years, but LCE also says that sometimes it was up to 100 years: depended on whether they were in a hurry to be adults or not.
But they reached intellectual maturity younger than
men: at around ten they were about as intellectually mature as full-grown Men (often more

)
Also, if they somehow were killed, they had the opportunity of being re-born, and thus getting a second childhood (during which they would progressively rember all of their former life).
They seldom were re-born thrice though (getting killed twice would seem a little careless perhaps).
The
Elves had less children as men, because:
a/ moch of their native power went into begetting each of their children (thus Míriel was exhausted after begetting
Fëanor, etc.)
b/their libido was indeed lower:
Doubtless they would retain for many
ages the power of generation, if the will and desire were not satisfied; but with the exercise of the power the desire soon ceases, and the mind turns to other things.
All to be found in Laws and customs of the Eldar, the Later Quenta Sil., Home vol.X (
Morgoth's ring) (from page 209 of the Harper Collins editon)