We always (well, nearly always) boarded first when our twins were in car seats - it can take a few minutes to strap the seats down, stow the bags, strap the kids in, etc. Of course, top-tier status practically guaranteed that we were among the first to board, even when no pre-boarding for parents with small children was permitted.

Aisles get clogged because clueless morons clog the aisles, not because frequent flying parents are allowed to preboard in order to stow their kids. Far too many people perform each and every activity while standing in and blocking the aisle with their fat ... instead of performing these activities while inside their row.