Present a written document outlining all of the issues, in particular the objections or worries that inevitably will be raised. Don't despair if your boss initially refuses. Rethink your proposal and try again. Job sharing does present difficulties that ordinary jobs do not, but none of them are likely to be insurmountable. You and your employer just need to be prepared to think your way out of them.
Some jobs are open to the possibility of telecommuting, part or all of the week.
Working from home can save time on travel and allow parents to be in the vicinity of their children while working. Like job sharing, telecommuting can be initiated by a written, well-considered proposal to your boss. However, it is worth being wary of the tyranny of technology. Bosses who have never looked after children themselves, may assume that you are doing nothing at home with the kids, and are thus available to deal with work at any time. If full-time work is the only option open to you, work hours can still be rearranged.