Tip number 3 - bring several props/diversions.
Kids have a short attention span and will quickly become frustrated with posing/smiling for too long. I suggest having a few things for them to play. This will add variety to the images, and more importantly, you'll have a much happier child to work with, as you can see from Tyler's face - concentrating on those bubbles.
Here's some suggestions... apples and other bright fruit look great in photos (but make sure you choose ones that are not too messy). Then toys (ones they haven't seen for a while) and even kitchen utensils... be creative! When you're close to finishing up, bring out the messier distractions like lollipops or cupcakes - but save them to the end or you'll be in for a wardorbe change...and possibly a bath!