number of years took to overturn Minersville s.d. v. Gobitis?

Question

a couple of Jehovah Witness kids did want to pledge allegiancetothe flag and later got in trouble.

Answer 1

From Wikipedia:
Minersville School District v. Gobitis, 310 U.S. 586 (1940), was a U.S. Supreme Court case involving a Jehovah's Witness named Gobitas (the name was misspelled), in which the court had held that Witnesses could be forced against their will to salute the flag. This decision had led to increased persecution of Witnesses.

Gobitis was overruled by West Virginia State Board of Education v. Barnette in 1943.

So, 1943 - 1940 = 3 years

Answer 2

Almost immediately, the Supreme Court realized that it had erred terribly in this case. Within months, Jehovah's Witnesses in the United States began looking for an appropriate test case to escalate.

Amazingly, that 8-1 Gobitis ruling was overturned 6-3 only THREE YEARS later. Perhaps more amazingly, this was right in the middle of World War 2 and in the face of intense patriotic fervor.
http://atheism.about.com/library/decisions/religion/bl_l_WVABarnette.htm

For decades, Jehovah's Witnesses have had an unprecedented role in establishing precedents for free expression in the United States.

http://jw-media.org/people/contribute.htm
http://jw-media.org/beliefs/society.htm