Hi Andrea,
I had a 45 gal drum that had been cleaned out and used to collect rain water,
It was really handy just pushing the watering can into the fully cut-out top of this drum when ever i wanted water.

One suuny hot afternoon i did just that "push the watering can into the drum But when i pulled the can out i found a young "Dove" dead in the can,

It had gone to the drum to get a drink and fell into the drum couldn't get out and ended up dead.

Now i have strong steel wire fixed around an old cycle wheel frame and everytime i use the drum for water i make sure that area is covered over with the wheel.

Why not go to your builders yard and ask for a wire frame as used for laying a concrete floor, (Solid steel)
you can cut this to size and place it over the pond,
it will hold a childs weight and you'll still be able to see the pond and all its glory.
But train the child to not play near the pond.

We have alsways had a pond , bc [before children] and when they were old enough to crawl/walk etc we always instilled in them that if they wanted to look at the fish they had to ask to go. then when we took them they always had to approach from the bottom of the pond not the rockery above it. the same with visiting nephews and etc. they very quickly learn, as long as you are consistent. as they got older I'd stand a little way away but in easy reach in case of accidents so they built up their confidence etc.

if you wish to fence it off then there are some lovely options available. my sister in law used cheap trellis laid on its side for the fence.

or you can get the steel mesh suggested above.

My OH made a wooden frame with support struts across the middle, and covered it with strong plastic mesh (the sort you use for clematis to climb up) It was not pretty but it served its purpose and one of the toddlers did in fact fall onto it, so it was a good job it was there. The frogs could get through the mesh and cats owls and herons couln't get at the fish, so apart from the ugliness it was win win. But the pond was only about six feet long by about five wide.

You can buy specially made metal grids to cover the pond for just this purpose, they can also protect fish from Herons etc.
Depending on what you want to pay some are flat but some are raised/domed and very decorative. Look at sites such as www.creative pondcovers.co.uk

They sound much more attractive than ours was Drc, but only possible if you can throw cash at the problem!