We are planning visiting London with two small children. As small children do, they might need to go to the toilet from time to time, and they need to go now!
Is it acceptable to ask buisnesses for kids to use their toilets, even if we are not customers?

What is the best way to find toilets while on the street (a good assumption would be that we will mostly stick to the more touristy regions)?

What to do when in a park? Is it acceptable for small children to pee (only pee) on trees and such in parks?