have 2 grandsons ages 2 & 5 around and would like to know if this plant is poisonous or not
It is not toxic to humans, but it is to pets. Generally, it is regarded as safe for humans. It is NOT edible, however.
https://www.gardeningknowhow.com/ornamental/flowers/rose-campion/rose-campion-care.htm
I want these to regenerate quickly. But also want fresh blooms. Do I dead head and let the old blooms drop in the soil to do this?
The old blooms on the ground won't regenerate unless they have gone to seed. Rose campion will reseed if the blooms are not deadheaded. So you can deadhead the first blooms but be sure to leave some of the last flush of bloom untouched so they will go to seed. They are hardy in zones 4 to 8, so they will come back from the roots as well.
https://www.gardeningknowhow.com/ornamental/flowers/rose-campion/rose-campion-care.htm