I owned 2 front mounted seats, 2 rear mounted seats, a long-tail cargo bike with multiple kid bike seats, and a trail-a-bike when my kids were small. I probably would've been better off with a trailer, tbh.
I never got a great solution I was totally pleased with. Front mounted seats were a lot of fun. We'd talk, I'd point things out, it was a great experience with my kids. However, they were less protective than the rear mounted seats if I let the bike fall over, and more difficult to use. Made even me nervous, and I'm a fantastic rider.
Rear mounted seats are ok, but we'd talk a lot less while riding, and my kids were stuck looking at my butt unless they looked to the side. I found the rear weight more difficult to handle than central weight.
Cargo bike is great in many ways, and I still use it for grocery shopping and stuff, but it's huge and heavy. Pedaling that thing uphill to preschool with my 2 kids on the back was rough.
Trailers provide better protection (slightly), they have use beyond the very short time your kids are small, they're stable, but it's a pain having the extra width and turning radius.
It was way better when my kids could hold on to a trail-a-bike and not fall off. We had some fun mountain biking then. Plus they started to pedal a little bit sometimes too.