Mentioned by www.kiddieholidays.co.uk
21 Things To Do In London With A Toddler For Under £5
"Get the lift to the top of 20 Fenchurch Street and let your toddler explore London’s highest public garden. There are 360 degree views of the London skyline, gardens to run around in and a café where you can buy cakes and pastries. Cost – Free, but you need to prebook."