In reply to Hooo:
The crazy current resale value of Isabikes makes them a no brainer (new or second hand). That resale value could change though. I don't like the narrow bars on the Islabikes and have swapped them out for some wider ones (cut down spares I had).
I'm sure that Frog bikes are excellent (not had any direct experience of them or had any friends with them, which says something), but I doubt they have the current Islabike kudos and associated resale value.
One friend did try an Frog for his daughter - but he said the top tube was longer and the fit (for her) wasn't as good as the Isla.
Another mate (same dilemma to you) was also looking at the Hoy kids bikes and was impressed:
http://www.hoybikes.com/kids
We did stray from the Islabike fold for a short while (20" wheel Ridgeback SX? rigid). Was OK, but our lad wasn't happy on it and complained of back ache and couldn't keep up with his younger brother on a lighter Islabike. Ridgeback - bought £220, sold £85. Enough said. The older lad is now on a 2nd hand Bienn 24 and loving it (and beating his brother, so order restored).
Post edited at 09:21