A father at a playground tells his small daughter to stop chewing her fingers and stay where he can see her. She cries, screams, and climbs onto the equipment looking as though she'd like to escape the park altogether. It's an ordinary toddler meltdown, but the speaker takes it hard.
The second half turns inward. He wonders whether he was kidding himself when he promised to be a good dad. His parenthetical admits what he secretly expected: to wave away every monster in the world, to give her everything she wanted, to make the world perfect. When he can't, he decides he's failing. Then the last line, "or is it just / that Jackie's two?", lets some air in. Maybe the problem isn't his parenting but her age.
The mood is rueful and a little funny, with real tenderness underneath. The short, breathless lines and casual "but yeah" sound like someone thinking out loud, caught between guilt and a hopeful shrug.