Yes - It's a completely dull and hardly newsworthy story. And yes - many parents have done something similar up and down the country and will continue to do so. However, this isn't just Joe Bloggs and his missus down the pub for a spot of lunch with their sprog. And despite the fact it is David Cameron who I really couldn't give a gnats chuff about, the main issue here is that his security detail = massive fail.
These people are providing protection to the most important politician in the country. They have procedures, tactics and drills which are supposed to be carried out to the letter whether it's just following him to the bathroom when he goes for a pee at a Tory party conference or doing the full drill at an all day/evening event in Europe somewhere.
The point is that it's not exactly professional looking when they realise 15 mins later after leaving the premises "Errrrm, hang on - wasn't the bosses daughter with us this morning when we left?". Especially in this day and age of heightened security threats. I expect someone's head will roll for this and quite rightly so.