I think there is a reason why 3 is still seen as a relatively normal family but 4 counts as a big family. It is a change.
This is copied from another thread but I thought is was relevant here too:
We only planned 4 but have ended up with 6 (accidental twins) and I love having a big family. I grew up with only one sister
I was 27 when I had my first which is quite old for a large family but then again I fall pregnant quite easily and this is different for everyone.
They have relatively big age gaps which has kept me slightly more sane except the last three are very close together. They are now 16, 14, 10, 6, 5, 5
All spontaneity goes out the window (especially since we don't have a car) but it is still crazy chaos most the time
You need to also think about practical and financial things. But don't let this stop you. Mine don't have all the latest gadgets that their friends do or the fancy holidays abroad every year but that doesn't mean they have less fun or less of a childhood iyswim.
(PS. camping is your friend)