We only have the one DD, but will now always go abroad for our main holiday at least.
First year she was born we stayed int he UK - went to Northumberland. Beautiful place - a week in june - spoilt as it poured with rain andwas pretty cold every day. Never again!
We have been to Italy when DD was about 16 months - fab place with children. The people adore children and will spoil them constantly, and they are welcome everywhere you go. Weather was beautiful. Disadvantages is that Italy can be expensive and can book up very quickly.
:ast year we went to Florida, when DD was 2y 4m - fantastic, but hectic.
This year are going to the South of France for 2 weeks. Have a car the whole time we are there so loads of freedom.
I would also say that we haven't found the planes/airport a hassle at all. DD i s so nosey and curious, she is intrigued by everything around her - and loves the chance to have her food on a cafe beforehand.
On the plane we always have a bag of goodies, and she is happy to look out of the window (although for Florida that was very boring - nothing but sea most of time). And she went for a little walk up and down the aisles, a few visits to the toilet seems fun at that age. LOL! And there are children's audio channels if you remeber to get a bigger pair of headphones before you go - acheap children's personal tape player will do.
On a plane, ask for you and your partner's food to be served seperately and they you don't need to juggle so much.