"Give them wisdom and devotion in the ordering of their common life, that each may be to the other a strength in need, a counselor in perplexity, a comfort in sorrow, and a companion in joy." -- The Book of Common Prayer
So Selah has developed the "Third Child Syndrome" - namely, that SHE'S the baby, and not you. And by "you" she means Kaity and Joe. Daddy and Mommy are not actually allowed to snuggle the big kids with suffering the consequences of Selah's squeals and complaints.
Here she's just verbally expressing her angst over Joe receiving the attention.
Now she has moved on to the physical stage of yanking on Joe's pantleg, attempting to dislodge him.