Here are the 4 and 5m pitched together for reference

https://www.facebook.com/photo.php?fbid=10157139724127329&set=a.10153578093912329&type=3&theater

We also have our size guide video that may help.

We're a family of 3 also, we have a 2 /12 year old! We use both 4 & 5m sizes, the 4 is great for long weekends, etc, but for longer term week or above I'd probably steer you towards the 5m size.

Think about future proofing, the 4m may be good for now, but as the tents should last a long time the extra space of the 5m may perhaps be appreciated as the family grows!