For a DIY alternative, you could try to create your own cactus mix by combining 3 parts of standard potting soil, 2 parts of sand or horticultural grit as well as 1 part of perlite. This will help ...
Mix up two parts of compost with one part coarse sand or grit. Choose plants with your children from the 'cactus' section at your local garden centre. Take care with the thorns and prickles ...