An amaryllis flower bulb can be purchased at Lowe's or Home Depot. With minimal care and water it should bloom around Christmas.
A beautiful poinsettia for them to enjoy throughout the holiday season. (Make sure they keep it out of reach of small children and pets. We've never had problems with our kids trying to eat the plant.)
Movie tickets and a certificate for free babysitting.
Lotions, soaps, or candles from a specialty store.
A Christmas ornament with a theme of friendship or whatever suits your fancy. A lot of families like to put up their trees over Thanksgiving holiday.
If you like to bake, make a Swedish Tea Ring or homemade cinnamon rolls for the family to enjoy the following morning. If the lady of the house cooked all day, she might want the following morning "off-duty".
If you choose wine, you could also bring some specialty cheese and crackers.
Best wishes for a happy holiday season!