Age 6:
Malik yanked the wooden figure out of Kadar's tiny hands, causing the latter to fall down on his butt and start crying. Malik turned away and crossed his arms over his chest, satisfied, until their mother came into the room, carrying a basket of now clean clothes in her arms. She frowned, taking in the scene, placing the basket delicately on the floor.
"What happened?" she demanded.
"Brubba took the doggie from me!"
Kadar wailed.
"Dog?" she asked sharply.
Malik reluctantly held out the little wooden dog statue that she had gotten him for his fifth birthday. "It's mine, and Kadar stole it." he said defensively.
"Malik, Kadar's only three." she said, taking it gently from his hands, "He doesn't know any better. Why don't you just let him play with it? Besides, your his older brother, and you're supposed to protect Kadar, not be mean to him."
Their mother handed the toy to Kadar, who's crying ceased abruptly. Malik glared at them both and stomped out of their room, past their disapproving mother, arms still crossed over his chest. He ignored his mom sighing exasperatedly behind him, and calling out his name.
Malik stormed down the hall, ignoring everyone around him, muttering to himself, "Stupid Mom. Stupid Kadar, thinking he can take my things. They're so mean to me. Mom and Dad probably don't even like me, and that's why they tried to replace me with Kadar. That's so unfair! What did I do to them?"
"Malik?" he heard someone say from behind him.
Malik's small hands balled into fists and turned slowly, stiffly, to look at the speaker. His father looked down at him somewhat disapprovingly, one eyebrow quirked questioningly. Malik offered no answer and just stared at him, waiting for him to speak.
His father sighed and pinched the bridge of his nose. He took Malik's hand and lead him to a bench in the courtyard where they sat in silence. Malik still had his arms crossed and the bitter thoughts continued to run through his mind. He glared pointedly in another direction, looking anywhere other than his father.
"Malik, are we cruel to you?" his father asked suddenly.
"What?" Malik asked, startled, shooting a sideways glance at his father.
"Are we cruel to you?" he repeated, "Do we starve you? Beat you unnecessarily? Have we cast you out into the streets to live as a beggar? Left you in some city somewhere by yourself?"
"... No." Malik said, wondering what his father was getting at.
His expression turned stern and he gave his eldest son a sharp thwack to the back of his head. Malik yelped and clapped both hands on his head not because it hurt, but because he was surprised. Still, that didn't stop him from giving his father an over exaggerated look of utter betrayal.
"Then don't ever say that your mother and I don't love you." he said severely, crossing his own arms over his chest.
Malik looked down at his toes, ashamed, getting his father's point. "I'm sorry." he mumbled bashfully, " I just don't want Kadar to take my stuff." he added earnestly, looking up, his eyes wide.
"Kadar is only three." his father said, expression softening slightly, "He doesn't know any better."
"That's what Mom said." Malik muttered, looking away and kicking at the dirt with his toe.
"Your mother's correct." he said matter-of-factly, before ruffling his son's hair and adding, "Don't you worry, Kadar won't be three forever and he'll grow out of it. You did, after all."
"I... did?" Malik spluttered, surprised. He couldn't recall ever going through such a phase.
"Yes." said his father, "A day did not go by when Altaïr did not come running to us, yelling that you took his stuff again."
"Really?" Malik asked somewhat timidly.
His father nodded. "Now, I suggest you go back to our room and apologize to your little brother."
Malik nodded, bit his lip, and nodded again before standing up from the little bench. He looked at his father, awaiting, expecting him to go back to the room with him, but he just shook his head and said that he needed to speak with Al Mualim, and that he had delayed enough already.
When Malik got back to the room, Kadar had abandoned the toy dog on the floor near his bed and was playing with some of his own toys as their mother put away their clean laundry with her back to them.
Malik picked up the dog and fidgeted with it in his hands for a moment before crossing the room and handing it stiffly to his younger brother. Kadar broke into a huge, goofy, grin with gaps where his lower canine teeth were growing in, that was sweet in a certain way at the same time. The three year old gently took the dog from his elder brother's outstretched hands and began to play with it.
Malik nodded, satisfied, and left the room once more, wondering if he could possibly find Altaïr to play with.
Based loosely on the short at the end of the bonus short at the end of the Fullmetal Alchemist manga, book fourteen.
Most older siblings probably experienced this feeling before. I know I remember feeling betrayed by my parents when my little sister was born, because suddenly they weren't paying as much attention to me any more. ;)