In reply to wilkesley:
The Decathlon bikes have a reputation as being very good value for money.
There are some websites that might give you more information.
Link below debates the merits of Triban versus others.
http://singletrackworld.com/forum/topic/which-btwin-triban-or-something-els...
Entering Triban in the search engine of the forum will reveal other posts re Triban.
Link below is well worth a read as it gives suggestions across the price range.
http://road.cc/content/news/72001-best-entry-level-road-bikes-under-%C2%A35...
It may be worth checking out local bike shops as this is the time of the year where they may be trying to shift 2014 bikes to make space for 2015 bikes. (Halfords are trying to change their poor reputation in the bike world by upskilling their workforce and the quality of the bikes they sell. It can be hit and miss regarding your local shop but it could be worth a look)
Would agree about being aware about not spending too much on a bike that might not fit for too long due to children growing quickly. It is, however, far more enjoyable for your child to ride a decent bike rather than half a ton of metal resembling the Forth Rail Bridge.
Happy hunting.
Post edited at 08:57