Q: My toddler ate a berry from this plant. Is it poisonous?
A: This is black nightshade, Solanum nigrum.
Several members of the Solanum family are considered poisonous to some degree….but tomatoes and potatoes are in this family, so not all parts are bad for you.
Here are some ID pix I found:
Here’s a description of properties:
And here’s a discussion of using the berries in pie:
I’m not a doctor, so I am NOT giving advice……but watchful waiting might be in order for your child.