Final answer:
The nurse would intervene if the parents make the child wear a helmet when riding a tricycle.
Step-by-step explanation:
The nurse would intervene if she observed the parents making the child wear a helmet when riding a tricycle. This is because a newly diagnosed toddler with a seizure disorder is at risk for falls and injuries, and wearing a helmet can help prevent head injuries. The other options, such as taking the child's temperature using an oral electronic thermometer, encouraging the child to play with soft toys during bath time, and making a peanut butter and jelly sandwich, are all safe and appropriate activities.