Don't feel like you will be offending them if you don't go because of DD1.

We had no kids at our wedding - for us, the reception wanted to charge adult prices for kids over the age of 2 and we simply couldn't stretch to accommodate the 20 odd kids that would mean inviting. We said no to kids, but the people who that effected either didn't come, or came to the ceremony and not the reception. I was not offended at all when people didn't come because they didn't want to leave their kids (and ours was a luncheon too, so no overnight needed).

As far as the registry goes, it's tricky. I'd find out if what you want to get them is appropriate, or see if they have listed something similar on their registry. We had a travel agent registry, and again, people didn't have to contribute if they didn't want to. DH's family got all funny about it (even sending us a nasty "anon" letter yelling at us about it) and kept bringing up the desire of me having a decent dinner set. I told three of them that I didn't want one, I had three and I didn't have the room to house a big one. They ignored me and bought me a massive dinner set, had everything right down to a matching gravy boat. I couldn't use normal cutlery on it, had to use pure stainless steel (which I didn't own). I was so angry, to be sitting there infront of them all, unwrapping piece by piece, after telling them it was something I didn't want. We never used it, and gave it away to someone who lost everything in the Vic bushfires.