Appropriate Thank You

Some flowers for your friend's wife and take them out to eat a couple of times to relieve her of meal planning. If a baby sitter is involved, insist on paying the sitter. They will love you forever.

Well, I live in NYC, so the first thing that comes to mind is to order to dinner in one night. It's hard when you have a baby to go out for dinner. So, I would check into ways to relieve them from dinner preparation and still not worry about the baby.

Whenever and where ever I stay with friends or family I always always take them out to dinner since that's one less night for them to have to worry about cooking for me, and one more fun night out for them. I tend to ask them to suggest the place since locals know best.. Some times I have to be sneaky so that I can get them to mention a nicer place as if I tell them I want to treat them some of them pick cheap places,, so I will just say " where is a nice place around here for a dinner out?"
Flowers are also nice, and perhaps if they have a sitter that you know of ( say they already have family near by etc) then I can also suggest a gift certificate for them to enjoy a dinner out after you leave , this of course doesn't work if they live in a small town since many places don't have gift certificates.

This is a great question! Paying for a sitter and dinner would be wonderful! i have many visitors come stay with me while they visit London. Frequently they like for me to be their tour guide which means spending the whole day in central London. While I don't have a baby I do have a dog and I would be gobsmacked and chuffed if my guests would offer to pay my dog walking fees. They add up.

Thanks for the suggestions as a single guy I fail to understand the parenting dynamic!

Maybe you could also offer to babysit one night for a couple hours so they can go out together, alone... ;)