In my opinion (taken from a gallup poll of me, myself and I) I would take a small child to BB. That noise and whooosh when the big wave pool lets all the water out really intimidated my smallest............and she was 6. Next trip we went to BB and I noticed it did look a bit more little kid friendly. Little slides pools etc. Have fun. Load up on sunscreen BB is very bright too.
I highly recomend BB over TL. BB has a wonderful children's area. The wave pool in TL scares me to death. I was in it with my then 5 year old neice and she was almost washed out of my arms. Unless a child is a good swimmer they could get in serious trouble if caught in one of those large waves. Obviously at 18 months you won't get into this kind of trouble. Playing around the edges is fun for the kids though.