Thank you for your question. I look forward to working with you to provide you the information you are seeking for educational purposes only.
Under CA law, you have to prove essentially that the landowner knew of a hazard on their property and failed to warn or failed to properly maintain their property to hold them liable for injury. The courts hold, “It is now well established that California law requires landowners to maintain land in their possession and control in a reasonably safe condition.” See: Ann M. v. Pacific Plaza Shopping Center (1993) 6 Cal.4th 666, 674 [25 Cal.Rptr.2d 137, 863 P.2d 207].
The courts find “The proper test to be applied to the liability of the possessor of land . . . is whether in the management of his property he has acted as a reasonable man in view of the probability of injury to others . . . .” See: Rowland v. Christian (1968) 69 Cal.2d 108, 119 [70 Cal.Rptr. 97, 443 P.2d 561].
It is well settled under CA law that a property owner is not liable for damages caused by a minor, trivial, or insignificant defect in his property. "This principle is sometimes referred to as the ‘trivial defect defense,’ and it is an aspect of duty that a plaintiff must plead and prove. . . . Moreover, what constitutes a minor defect may be a question of law.” See: Cadam v. Somerset Gardens Townhouse HOA (2011) 200 Cal.App.4th 383, 388–389 [132 Cal.Rptr.3d 617].
Additionally, the CA courts emphasize that the liability imposed is for negligence. They state that "the question is whether in the management of his property, the possessor of land has acted as a reasonable person under all the circumstances. The likelihood of injury to plaintiff, the probable seriousness of such injury, the burden of reducing or avoiding the risk, the location of the land, and the possessor’s degree of control over the risk-creating condition are among the factors to be considered by the trier of fact in evaluating the reasonableness of a defendant’s conduct.” See: Sprecher v. Adamson Companies (1981) 30 Cal.3d 358, 371 [178 Cal.Rptr. 783, 636 P.2d 1121].
So you must prove the landowner failed to use reasonable care to keep the property in a reasonably safe condition. A landowner who owns/leases/occupies/ controls a property must use reasonable care to discover any unsafe conditions and to repair, replace, or give adequate warning of anything that could be reasonably expected to harm others.
You can send a demand letter at any time if you choose.
You can represent yourself, you cannot represent your child. The claim here is your child's claim and as such it requires you have an attorney represent him, if not it would be unauthorized practice of law for you to do so.
You can hire a personal injury lawyer, they work based off of a contingency fee, meaning they will take a fee when they obtain a judgment/settlement in the case.