Re the weather "There is NO way to tell until the day or maybe the day before."

We have these neat things called weather forecasts. You can find them online, on TV and on various apps. They are usually pretty accurate and will provide a good idea of the weather by location 5-10 days out. Some, will show the weather for a location on and hour by hour basis. If the weather is a concern, have a couple of options in mind have a look at the forecast and decide closer to the time.

I really meant there is no way to tell now or even probably by the time they fly out -- so I would not pre-plan a major out of town trip now. I was in London at the end of Dec / early Nov and all the forecasts did indicate rain and cold whereas it was dry as a bone and I barely needed a coat some days. So while forecasts truly have improved a LOT, one really doesn't know until close to the date.

Canterbury on the train maybe? St. Albans? A day at the beach in Brighton? British seaside towns are totally different to anywhere you've been probably :) Although don't expect much from the weather in March...

One of my favorite day trips out of London was taking a train to Salisbury, touring the Cathedral, then meeting a private driver/guide to explore Whiltshire with visits to Stonehenge, Avebury and seeing the general countryside.

Windsor and York.