It is the access to the town of Akumal (4 minute walk) that distinguishes ABR from the Oasis Akumal. The beach and snorkeling are terrific at both. The access to town if staying at the ABR allows you to perhaps catch a meal or two in town if you get bored with the food (we usually stay 10-14 days so after a while the buffets get a little old).
Though I haven't been to the Oasis in a while, I did stay there 3 times, so I remember the food as being good not great. The same could be said for the ABR, though I would give a slight edge to ABR on the food as well, mainly due to a little more selection.
I think you have more of a chance of getting an ocean-view room at the ABR than the Oasis, although at the Oasis you are never a far walk from the beach either.
Also, the Oasis Akumal has recently expanded and so is now a bigger resort than ABRm, and we prefer it small.
I can't speak to a crib, as we never required one for our daughter.