Fodor's Travel Talk Forums - Legoland Windsor on day of departure

I'm going to be in the UK for a week or so in September and was looking at going to Legoland at Windsor on the last day before a 9PM flight with my wife and 2 kids (5 and 7). We are staying at a London hotel. We will have suitcases and carry on bags that need to be stored while we are at the park.

I'm tossing up between a private airport transfer that stores the bags while we are Legoland (such as London Cruise Transfers) Vs going to Heathrow early and either checking in bags and using left luggage for carry on bags (although I don't know how long this would take and don't want to eat into Legoland time) or storing all bags at a left luggage service (a bit pricier but likely faster).

What would be recommended in this scenario ?

Also if using a transfer service that stores the bags for the day how to people answer when checking in if the bags have been out of our control since we packed them ?

Changing to a Legoland resort hotel isn't an option as we are quite busy in London the day before.