Can anyone please identify this plant/weed?

[SummerinKansas]

Son has woken with an allergic reaction. Turns out him and his brother were playing with the pods of this plant yesterday.

I’ve figured it out thanks with some help from friends. It’s Caper Spurge

Spurge is another name for Euphorbia, it comes in several varieties and is known for its irritating sap.

Try antihistamine tablets or cream, if you're getting worried about the severity go to Minor Injuries.

Be aware that it can turn the skin sensitive to light, so the rash may recur in future summers. I have a patch on my leg that I completely forget about, but it recurs for a few days in early September and reminds me that it's there.

A useful lesson to the boys that some plants are harmful, that they need not to mess with the harmful ones, and they need to learn to recognise them. You can never ensure that they'll not come into contact with things, so while you can try to keep them safe in your garden, only their knowledge will keep them safe when they're elsewhere.