We've been to both Typhoon Lagoon and Blizzard Beach with our boys (last visit they were 4, 2 and 1) and BB wins hands down for the little ones.
TL is geared towards older kids / adults and has only a small area for the little ones. Plus, one thing at TL that really bugged my two youngest was that the kiddie area has these permanently mounted water blasters which kids can shoot at one another and my boys hated being sprayed every so often. They didn't want to stay at that spot and there weren't many other areas for them to play in.
The main wave pool at TL is definitely off-bounds for anyone under the age of 10, in my opinion. I watched DH get knocked off his feet a few times (by either the water or by being bumped by other people) so I can only imagine what would happen to a small child.
The family raft ride at BB is awesome - possibly a bit fast for some kids but we held the boys snug against us and it was a total gigglefest for them. We rode it 6 times!
We brought a waterproof disposable camera (bought at home - much cheaper that way!) to BB and got some great pics. There are also a bunch of Photopass folks around so carry your Photopass tag on a stretchy wrist thing to make it easy to use.
The family raft ride at BB:
The kiddie area:
Kiddie inner tube slide in kiddie area - that's my 2 year old coming down. The lifeguard catches them at the bottom (they're going pretty slow) and gives their tube a nudge towards the stairs (the water is very shallow and only one kid goes down at a time - there's a lifeguard at the top of the slide who monitors it)