The grownups tell me that I look Exactly like my doll, With yellow curls and dimpled cheeks And big blue eyes and all.
I can not blame the grownups Who've looked at us and smiled. Of course my doll takes after me, Because she is my child!
A little girl has noticed that grown-ups keep saying she looks just like her doll: yellow curls, dimpled cheeks, big blue eyes. Most people would take that as a comment on the doll, which was made to look like a pretty child. The speaker sees it the other way around. In her mind, the doll is her daughter, so of course the doll resembles her. Children take after their mothers, after all.
The humor comes from how seriously she reasons this out. She isn't offended or confused; she's gracious, even a little patient, saying she can't blame the grown-ups for smiling, since they simply haven't understood the family relationship. The title helps, because it tells us from the start that she sees herself as a mother, not a plaything's owner.
The mood is light and affectionate. The poem gently pokes fun at the child's confident innocence while also respecting it, letting her imaginative world stand on its own terms.