You get caught taking pictures of children around here without consent and the police questioning would be the better thing that may happen to you that day. Most parents around here guard their children like a momma bear guards her cubs...and some of them mamma bears carry guns.
U.S. law is very much alike, a street scene with people doing normal things, I wouldn't ask everyone for permission, but I would do it openly to give anyone a chance to vacate, turn, or object. I'm not out there to make enemies or be known as, ''that creepy guy with a camera''. If an individual is interesting, ask, talk to them and mention you would like to photograph them. Those videos I suggested are a wealth on ideas to get to photograph people on the street.
I agree that, when it comes to children, discretion is warranted although that doesn't preclude taking a shot.
Momma was there for these shots.
OTOH, this little girl was by herself and clearly waiting for someone. I was on the opposite side of the street, found her to be an interesting subject, and had no qualms about capturing the image.
For adults, I prefer candid shots, although I had a nice chat with the man in the chair before I took the shot of him.