Please discuss any questions with your own network of professionals, friends and family first. I couldn't afford to go part time a few years ago. There are several ways in which one can change their work hours to meet the needs of family, from going part time to working a variety of flex schedules.
Some people even supplement their part time or flex schedule with telecommuting hours.
See the telecommuting FAQ for more information on this option. In general, full time is considered to be 40 hours per week or more, while part time usually ranges between 20 and 32 hours per week, although other variations certainly exist. Flex time is usually talking about full time hours, but either on fewer days with more hours per day, more days with fewer hours per day, or even a five-day schedule with shifted hours. No, it's never too late to go part time if that's what you want to do. Working part time with school aged children has it's benefits in terms of helping with homework and other after school activities.