If the old cover is shot, why not buy a new one? Ours became waterlogged, so very heavy to open, and the thermal retention was terrible. A new one locally was >$600, but I found one online (Canada: Lillypad Cover Company, hot tub covers, Delta, BC) with MUCH better specs for ~$500 with delivery. I'm in Canada where heat loss is probably a lot more critical than in San Diego.
The new cover is thicker, better fitted than the factory original, and includes four locking clips.
With regards to child security, ours is above the deck so hard for a small child to even see into when open. I built an step stand with a railing and one front wheel that an adult can easily move to provide access.