Just to put the opposite view, as a till operator I really like the challenge 25 policy. It's very hard sometimes to judge if a person is under 18, 18, 19, 20 etc, especially young women who may be heavily made up. If I sell to someone underage I can be personally fined, lose my job, and potentially go to prison. Challenge 25 provides me with a little bit of security to be able to (nicely) say "yes I think you're probably over 18, but you look under 25 to me so I need to see some ID please". People who strop about it don't really impress me, especially the ones who say "but I'm fucking 23!" Well done Einstein, I've done my job then because you're not 25! I had a guy a while ago who had a similar strop, and I said to him "Well I'm 47 love, so you look young to me". His answer was "You don't look anything like 47", and I replied "Well you've just proved my point that it's hard to judge people's ages sometimes" 
Also, re the wanting your child to hand over your winning lottery ticket, choose your lottery numbers or scratch cards, they are not 16, and given a choice between disappointing them or losing my job and not being able to pay my bills, it's a bit of a no brainer for me. And I say that as the parent of a four year old who would also love to do lottery tickets 
I'm not saying some of the rules (teaspoons, vanilla essence, etc) aren't stupid, but it's not the cashier's fault. Complain to management / government if you don't like the rules, not the poor sap who has to enforce them.