Assuming you have a partner, each adult has two kids on their bike (one front seat, one back seat). At 6 the eldest can even cycle by themselves if you push. I'm Dutch and this is completely normal here.
Edit: with kids 6 miles is a stretch, not that it's super hard, but you'll often be tempted to just take the car. If you upgrade to an e-bike that temptation will be a LOT less.
I used to have this bike with an extra front seat and regularly cycled places with 4 kids (4-7) by myself (pushing one on their own bike): https://kokfietsen.nl/image/cache/data/Azor%20Catalogus/069-...
But then again, this country is really flat.
Edit: with kids 6 miles is a stretch, not that it's super hard, but you'll often be tempted to just take the car. If you upgrade to an e-bike that temptation will be a LOT less.