We and our 3 year old had a great time at Sealife. The staff we spoke to were all really helpful and knowledgeable about the exhibits.
My only complaint is the cafe which lets it down. We'd have stayed longer but we had to leave to have lunch. The cafe seating area is frankly disgusting. Sticky uncleared tables full of used cups and empty crisp packets meant we would have been unlikely to eat there anyway even if it hadn't been for the poor choice of food and high prices. Really lets down an attraction of this standard.