Toddlers and preschoolers have an attention span of around 10 - 12 minutes, and once its exhausted, learning and listening are no longer fun for them. So when it comes to story time mix it up a bit. Use one or two of these ideas for each book you read and make story time as fun and as interactive as possible.
Try stepping back when your kids complain about feeling bored. This will empower them to think for themselves and learn to be resilient. It will also encourage them to find their own way out of the boredom, and the problem-solving process helps them feel good about themselves.