When we have flown Delta, we have been allowed to pre-board after those with medical issues.
When we traveled with car seats, we would split up. DW would board early with carry-ons and car seat to get settled in the plane. I would take the kids to the restroom one more time, let them move around, etc. Then board at the last minute to reduce the time they were sitting there on the plane.
Now that both kids are mobile and can carry their own backpacks, we prefer to board as late as possible.