Fire ant baits are considered safe for humans and most animals. The bait used to treat fire ants is specifically targeted to kill ants.
The active ingredients used in fire ant bait are non-toxic to humans.
The ingredients will not be absorbed through the skin by walking on grass that has been treated with bait.
If granules have been spread across a yard using a handheld bait spreader, utility terrain vehicle (UTV) or helicopter, it is very unlikely that a child would be able to find individual granules in the grass.
Even then, it would be almost impossible for them to consume enough bait to make them sick.