On Siblings

I watch as they negotiate
What each of them can claim,
Announcing something's "Mine!" appears
To be the only aim.

Whatever one is playing with
The other wants as well,
Despite the fact it's not a favorite,
Far as I can tell.

Yet in the market, a surprise - 
The older made his picks
Including items for his sis - 
No envy in the mix.

Just watching out for her, he was
The most attentive brother
For that's what siblings are - 
Both friends and rivals to each other.