If they arrive early they ll have a lot of time to visit the museums.
If the weather is fine they ll walk during their staying.
If it's cold they ll not stay out for a long time.
If it rains they'll take an umbrella and go sightseeing.
If they go fishing they'll have a lot of fun.
If they visit their friends they'll be very happy.
If they stay with their grandparents they'll find out more places to explore in London.
