If you are close by, ask them if it would be okay to make something for the house and ask if they would like to pick it up. I wouldn't show up at the house unannounced or uninvited.
If they aren't super close geographically, mail them goody packages, with cookies, candy jars, magazines (you can also buy subscriptions for the house - a gift that keeps on giving and that everyone can enjoy), movie DVDs (or Blueray - whichever player they have), Netflix subscription, video games.
You can also make different packages based on holidays. Halloween goody bags, "Winter holiday" stuff, exam time.
You might also ask the boys what they might like or want. If you have a specific price range, price a few things out and have them choose.
I think it's nice to want to support them, but just let them think it's on their own terms.
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