One old enough to be admitted to Communion should be old enough to be "responsible" for trying to go to Mass. For most young ones this would mean asking the parents or another trusted adult to take them.
This is different from being "culpable" in the event that their requests are rebuffed. Certainly, at some point in the child's further development they become masters at getting driven to school dances and football games and the mall to be with friends. When the child is at that point, he certainly has the means to arrange transportation to Church, should he desire it.
SD
Absolutely. My comments earlier were meant in terms of much younger kids who are none the less ready for the sacraments. It's a good habit to get into, even the little ones who can't take themselves to church, to ask and be concerned.
Its difficult to believe, based on experience, that many of these children asked to be taken to Mass. The fruit does not fall far from the tree.