Tents by Berth
When choosing a Family Tent always pick a Tent at least 2 berths larger than you need. Manufacturers generally size the tents by the number of People they will sleep on the ground with no Airbed or Camp bed. So you need to account for this, as well as storage for your clothing and belongings when you pick a tent.
In the UK we are not renown for our Hot, Sunny Weather, so make sure the tent you choose is big enough for all the family to relax inside, especially with young children you need space.