Triathlons are best for singles with lots of time, or triathletes married to each other
If you have a family, train with your spouse and/or your children as much as possible. My wife and I swim together.
Other tips to minimize your time away from family: run and bike from the home; run or commute to work on your bike, run or bike during your lunch hour, limit time spent training with groups (group activities inevitably add a great deal of time for traveling and socializing), compete in short triathlons requiring less training, and maintain your bike yourself.
Organize your training and competing schedule in regular consultation with your family. Be flexible and make adjustments to family priorities and the demands of work.
Put family needs first when working out a balance between training and family.
Treat the trip to triathlons as a mini-vacation for the family and take the opportunity to sight see and enjoy the travel. My wife was happiest if we stayed in a good hotel.
Maintain a long term perspective. If it is not practical to prepare for a full length Ironman now, you should be able to fit it in after the kids are grown, or you retire, or have a less demanding job.
Unless you are independently wealthy, take care in what you buy in the way of clothing and hardware for triathlons. Much of what is available is great for eye candy but expensive and of little marginal benefit over good products at reasonable prices (see General Advice).