Is becoming angry, raising one's voice, and punishing siblings who do not maintain Fajr prayer considered a sin or an injustice?

Being negligent in prayer, especially Fajr, is a grave error and a sign of hypocrisy that many have been afflicted with. Your advice to your brethren is a duty for which you will be rewarded, so continue to advise with kindness and gentleness. Remember that prayer is not obligatory until puberty, which is attained by seminal emission, growth of pubic hair, or reaching the age of 15 years. For females, menstruation is an additional sign. Whoever has not reached puberty is commanded to pray to accustom themselves to it.