Buy T-posts and hardware cloth plus 2x4 inch wire for the roof. That'll be the strongest easiest way. Lay wire flat on the ground to make an anti dig skirt. Although I agree you'd do well to consider electric. Commercial electric fencers are rated to be safe for a 2 year old child. I raised all my kids with hot wire nearby. They rarely touch it twice lol.
But really, kids learn safety rules.
But really, kids learn safety rules.