It's a common question and one that should have an answer, but there is not much that can be done to eliminate ants that are living in a sandbox. Of course, it does not appear that the ants cause any harm, and peaceful co- existence is probably the best approach. But for many parents and caregivers, allowing children to play in ant-infested sand is more than they can bear.
Obviously, the traditional ant control insecticides used in the lawn and garden are not appropriate. One possibility, however, suggested with great reluctance, is to remove the sand, treat with diazinon the underlying soil where the ants are nesting, wait a month and then return the sand.
My only other suggestion is to try an un-researched technique mentioned in organic gardening references. Soapy water, used as an insecticide on soft and slow insect pests, may be toxic to ants. You might try pouring a solution of soapy water onto the nest area of the soil after the sand has been moved aside. Mix 1 tablespoon of liquid dishwashing detergent per quart of water and drench the nest area. One reference where I have seen soap mentioned for ant control gave this explanation: the drench "will kill some ants and cause the remainder to move their nest away from the treated area." Maybe.
This article originally appeared in the June 8, 1994 issue, p. 85.