Research local schools in your neighborhood. Figure out what schools are there and what programs they have. There are many that have bi-lingual or English as a second language programs. Ideal would be so-called "two way" program: half of the kids are native English speaker, the other half is native Spanish and the instruction language alternates every months or so.
Once you find something that may be a good fit, just go over there and ask. Have a conversation and see where it goes. If you don't like the answer from a particular school try another one. You may have to sort out insurance, liability, transportation, food, etc.
We have done this the other way around: US kids attending a public school in Europe for a while. The school just said: "Sure, no problem" and it was a good experience for all parties involved. There is more school to school variability in the US, so you may have to try a few different ones.