Does the crime of child endangerment under Penal Code Section 273a (a) require a willful intent to cause the injury or endangerment?

Yes. An element of child endangerment is that the defendant willfully inflicted or permitted unjustifiable physical pain or mental suffering or endangerment on a child. This crime does require a willful intent to cause the injury or endangerment. It is unlikely a reasonable mistake would satisfy the elements of the crime child endangerment under Penal Code Section 273a (a).