K.A.
The first time we took the kids to Disneyland we only had our first 2 children. They were 1 1/2 and 3 1/2. They LOVED it! When we added our third child we took her when she was 17 days old.Albiet, only fora couple hours, we only did one ride and took the kids to Build A Bear for their special "big brother" bears. It was a special gathering day of a huge group of friends planned before we were pregnant so we went to quickly say hi and ride Small World. We have had annual passes since that very first trip and they love going. They are now 9 (he'll be 10 in Feb), 6 (he'll be 7 in 17 days!) and 18 months.
Best tips I have. Use those fast passes! Most people don't know that you can still use them after the end time. So long as the beginning time has arrived you can use them any time up until closing. You can get a new one after the start time of the other one I believe the system is so you can have multiple valid ones on you at the same time. Lines shorten for the big rides during fireworks, shows and parades, some to just walk on. Obviously you'll want to see those on your trip but staggering them between days and not watching them every day gives you the opportunity to take advantage of that. On the flip side, right after the fireworks people litterally run to get into line at Space Mountain. Lines shorten at meal times, if you can stagger your meal time to be off from the masses (don't eat dinner right at 6 for example) you can avoid the lines at the restaurants and the rides. Crowds at the holidays are crazy busy, be prepared. Get places early for a good spot to watch shows etc.
I love, Love, LOVE Disneyland at the holidays! I take the crowds in stride and go with the flow. We're going in a bit here ;)