Can I sue if my 9 year old son and husband went on a school trip where my son suffered a laceration to his ankle while swimming in the hotel’s pool?

Yes, you could sue because the injury was caused by the negligence of the hotel and there probably is no liability on your son [some states require children to be older than a certain age for them to be consider negligent at all] [your husband might also be able to sue in California for his emotional distress since he was in "the zone of danger], but aside from payment of the medical bills and maybe a few hundred dollars [assuming no permanent injury such as a scar], the case has almost no other value. You would have to sue where the injury took place or the state in which the owners of the hotel are incorporated. In California, you could sue in Small Claims court, but they normally give little for emotional distress.