We also do 3 and 1. I think having a full row to your family group is a big advantage regards spreading out and not having to take care not to invade others' space. Also both children can get up and down without having to go past anyone else.
When we flew to South Africa back in February we were lucky to have a whole middle row to ourselves. On the connecting flights we sat one adult and two kids and one adult by themselves. That way one of us could get a rest!