When dd was having her birthday party i served fizzy drinks as having read the labels on the carbonated drinks and also on the squashes and 'kids' drinks i realised that the fizzy drinks had far less shite in them in comparison to the drinks marketed towards kids. Every single cordial had aspartame in it whereas 7up and fanta are basically just water, carbon dioxide and some veg extracts.
My 5 and 3 year old are allowed a half glas of 7up with popcorn and a movie every now and again too, it's a treat for them and i see no problem with it.
Not only that but when they have vomiting bugs it's handy to have some 7up in the house, it's generally the only liquid they'll keep down. [shudders at memories of vomited smoothie, milk, water and juice courtesy of ds1 this weekend]
and as for the cafeine... mine drink tea and coffee too, it certainly doesn't have any adverse affects on them (unlike chemical addictives which send dd up the walls) so i see no harm, they love sharing my tea and coffee.
My mother gave ds1 a taste of wine recently too... cheeky sod loved it and kept asking for more 'red juice'... she was counting on him hating it like me