The younger kid is always bothering the older kid when he is playing.
The little brother is always getting in his big brother's hair when he is playing.
ーThe younger kid is always bothering the older kid when he is playing.
「下の子が上の子が遊んでいるのをいつも邪魔する」
to bother で「邪魔する」
ーThe little brother is always getting in his big brother's hair when he is playing.
「弟がお兄ちゃんが遊んでいるのをいつも邪魔をする」
to get in someone's hair で「人の邪魔をする・人を苛立たせる」
例：
The younger kid is always bothering the older kid when he is playing, so they often end up fighting.
「下の子がお兄ちゃんがいつも遊んでいるのを邪魔するから、よく喧嘩になる」
to end up fighting で「（最終的に）喧嘩になる」
ご参考まで！
カナダ 
