Children love cycling. It's time spent with you, talking together, discovering things and enjoying fresh air and exercise. They pick up on your enthusiasm. And as they get older, a bicycle is their independence long before the first motor vehicle comes along. If one of you is an experienced cyclist, buy your other half a reasonable bike one of a quality you'd consider for yourself, even if it's different from the kind of bike you'd choose. Keep it running as sweetly as one of your own, giving it a spin around the block periodically to check things are all as they should be.
On family rides, let the less experienced partner set the pace and the mileage, and level the playing field by fitting the trailer, child seat or luggage to the more experienced riders bike. Stay away from busy roads, which are intimidating and prevent conversation due to noisy traffic.
Younger children won't need much entertaining, but they'll want to stretch their legs, so aim for somewhere with a bit of grass or a play area. Keep mileages low and take plenty of snacks and drinks.