Final answer:
The boy's family is most likely to sue the Gregors for negligence, based on not securing their pool, which is considered an attractive nuisance that should be protected from unsupervised access by children.
Step-by-step explanation:
The boy’s family will MOST likely sue the Gregors for negligence. In many jurisdictions, homeowners have a duty to ensure that their property is reasonably safe and secure from foreseeable harm, even for trespassers. The fact that the Gregors did not put up a fence around their pool could be seen as failing to take reasonable steps to prevent foreseeable accidents, such as a child being attracted to the pool and getting injured.
This concept is particularly relevant in the case of 'attractive nuisance', a legal doctrine that might apply here. An attractive nuisance is a potentially dangerous object or condition of interest to children, which owners are legally obligated to secure. Pools often fall into this category, and homeowners typically are expected to take measures such as fencing to prevent children from accessing them without adequate supervision.