Let's start with the basics. Legoland Windsor is bigger than you think. It's impossible to do it justice (and get your money's worth) in a single day. At most you and your family will cover around half the things to do in your allotted seven or so hours. Much of your time will be spent queuing up for things. So think seriously about getting an 'annual pass'. For once, this isn't just a theme park's marketing spin, it really will save you money if you plan to visit more than two or three times in a year. And the kicker is that once you've got annual passes for your family, it's very tempting to just turn up there for a few hours, for the whole day, whenever, simply because you can and because it's all basically free thereafter. If you live within 50 miles of Legoland, go for the pass, every time.
Secondly, note that a lot depends on the age of your children. If you have sub five year olds, they won't be able to copy with more than a third of the activities and you'll end up with tired children before the end of the day and a feeling of somehow not having gotten value for your money. If your children are this age, make sure you go for the annual passes, as mentioned above. That way, you can leave whenever you want to and go back as many times as you'd like to, doing different things each time, without it hurting your wallet too much.
Again mostly applicable if you have younger children (say, under ten), take a couple of towels and their swimming costumes. The Duplo world water play area is fabulous fun on a sunny afternoon and trust me, your kids will want to join in. In fact, they'll want to strip off and join in even when the weather's rainy (been there, done that). So be prepared!
Save yourself a LOT of energy at the end of the day by planning to make the final trip up the hill to the entry area using the Hill Train, which goes from the centre of the site. As long as you don't leave this too late (it gets popular), this make all the difference between a happy and a weary family.
All text on these pages is Copyright Steve Litchfield, 2005, 2006, 2007