My children may have gotten some weed killer on their hands. We washed them immediately but are there any other precautions we should take?

Avoidance. Keep poisons away from kids.

Read the label. Every weed killer will have information as to what to do written on the label. If not, call your local poison control center with the information on what brand of weed killer you were using. There are many different brands, and the kind of toxins and their concentrations may vary between these. Generally, thorough washing with soap is adequate, but again, read the label and follow instructions.