Are children more susceptible to lead poisoning?

Yes: Lead exposure is bad for anyone, but for children, who have brains that are not fully developed, it's worse. For every measurable increase in blood lead level, there is a corresponding and measurable decrease in intelligence quotient. Further, children, especially toddlers, are far more likely to put lead containing things in their mouths, and thus poison themselves, than are adults.

Yes: Sure. They are the ones picking stuff up off the floor and putting it in their mouths. Adults can also get lead poisoning if they work with lead products, it's fairly prevalent in gunsmiths who pack their own ammo.