I have all of mine up on tables from Ikea.
Once you have the dimensions of the cage then go online and look at table tops until you find one that is slightly larger than your cage, and will fit into the space you have.
However please be aware that whilst this may keep them safe in the short term, it could actually cause a bigger fall from a greater height if your son works out how to pull the cage off the new table.
I underdstand that it is difficult with young children, but you also need to work on keeping him away from the piggies cage unless he is supervised so you can make sure he understands the dangers of pulling their cage over (for both him and the piggies).