Staff in supermarkets were told a few years ago not to hold the hand of a lost child or touch them in any way in case they were prosecuted for assault.
A friend of my ex' worked for ASDA and apparently the story went round all the stores that an employee was being prosecuted for 'guiding' a child round the store in search of his mother by placing her hand on his shoulder. Mother was found and child handed over with a cursory "Thanks love" sort of comment. Next day the police turned up to question the employee stating the child had a bruise on the top of his shoulder. Investigations took place and it turned out the child was one of those people who bruise very easily. Case was eventually dropped but it then became the norm that no employees touch a child/hold their hand etc for fear of litigation. The only acceptable reason would be to prevent them from immediate danger such as running into a glass door or similar incident. If I ever see someone apparently lost I stand well back and ask them. If they say yes I ask another member of the public to alert staff while another stand with me at a distance from the child. Protects the child and protects me to have an independent witness.
As for opening doors, I always hold a door open and if they say thank you I say, "You're welcome." in a polite manner with a smile. If they don't I say it anyway but with heavy sarcasm. LOL