DD's 2 and 3 year old trips are my favorites. Everything was real and magical. It was so fun watching her on those trips, and she absolutely loved WDW. By kindergarten, they have clued in to reality- and if they haven't, their kindergarten friends will be sure to clue them in.
We did one week long trip when she was 2 and we went for 2 separate week long trips when she was 3 (the year of big discounts). They are definitely not too young to go. It doesn't matter if they remember it because YOU will remember it - and those photos will last a lifetime. I don't get the whole won't remember thing. By that standard, they probably won't remember their first few Christmases or Birthdays either, but you don't just say- oh we won't buy them presents or celebrate because they aren't going to remember it anyway. DD(7) does still remember quite a bit from that first trip. She's been every year, so you would think it would all run together by now, but she is still pretty good at telling us what happened on which trip even when DH and I can't remember.
Our school age trips are fun, but they aren't totally magical and awe-filled like when she was small and everything was real to her.
That said- I only had one that age, not 2, so I can't speak on that! Ours was actually better behaved at WDW than she was at home. She was an extremely high energy kid so the pace of WDW worked great for her.
I will say though that at age 2 and 3, DD didn't care for AK at all. Her absolute favorites at that age were (and still are), MK And EPCOT. The reason she didn't like AK is probably because we have a really good zoo at home and she really didn't see the difference and didn't want to waste her time at the "zoo" when she could be riding rides and visiting Princesses. She was begging to leave AK and go back to MK or EPCOT by noon those 1st 2 years. If you don't have a great zoo at home, your toddlers might love AK.