May I ask where you are in Zone 5 that these ants exist? Once we establish that these are definitely fire ants, we can work on a good solution that will be safe for the children.

Here is a link that might be useful: {{gwi:1154963}}

Western MA.
They are red ants, with my VERY limited knowladge of ants, fire ants are the only red ants I'm aware of.
Thanks.

There are other red colored ants, and fire ants don't exist in MA, lucky you.

I'm not sure of the feeding habits of your particular kind of ants, so really can't recommend a bait. You might want to give your local extension office a call to ask them about the reddish ant you have in the sand box. They would be in a good position to know what species of ants are common in your location and what to do about them.

I'm not the bug expert here ;-), I'm lucky to know what I find in my own climate...

But it's raining, I had some time, and came across this bulletin from U of Maine about European fire ants as opposed to the South American kind.

I can't help with how to get rid of them. One site I saw said for childrens play boxes to either change out the sand or spray thoroughly with vinegar. If these are biting ants, children present, I might want to be more proactive than vinegar :)

Here is a link that might be useful: U Maine - European red fire ant

"local extension office"?

I don't know if they bite or not. I'll probably take a closer look at one, and if possible take a close up pick of one.

Thx

A local extension office is an extension of your university. A good place to turn for advice in your specific region for gardening and outdoor related questions
(plant diseases, soil analysis, insect identification, noxious weed lists. Also nutrition information, safe food preservation at home like canning guidelines, more.)

OT - the suggestion brought back a laugh ;) MANY years ago when first married, my sis mailed an insect sample to WSU extension office, there was no office convenient to her home. The letter she got back said something like Dear Mrs. XXXX....We would have been happy to help you with the identification of your sample but they were crushed beyond recognition by the stamp canceling equipment. She'd mailed them in an envelope, they arrived as dust.

Here is a link that might be useful: MA, UMass offices

I can remember red ants that stung as a child in the 1940's, but have not heard them called fire ants before. Since all ants are related, these may be something similar.
If these ants are nesting in the sandbox you may need to dump te he sand in there and replace it with clean sand. That would be the fastest way to solve the problem. You could also make a screen and sift the sand in there now which could, depending on the mesh of the screen, remove the ants including the larva and queen of there is a nest.