There is an old saying that, "Grandchildren are the reward you get for not killing your kids." I think most of us that have survived the agony and joy of raising children can understand the humor in that saying. Now we look forward to the joy (without the agony) of watching our grandchildren grow up. And I suspect most of us grandparents also subscribe to the theory that what makes it agony free is that at the end of a joyful day with them we can give them back to their parents for the agony part. That is all well and good, but we need to avoid making some common mistakes that can make the agony for them any worse then it naturally is.
The first and most important mistake to avoid is to forget your role in this relationship. It is important to remember that you are not your grandchildren's parent. You do not have a first claim on their time; that is a privilege reserved for their parents. As difficult as it may be to accept; you are at least second, and as they get older you may find that you are third or fourth at best. Accept it and do not insist on making demands for time that make it uncomfortable for them. You also should never offer unsolicited advice on anything related to your grandchildren. If your children or grandchildren want your advice, they will ask for it. Trust me, no matter how sure you are that you have the right advice, keep it to yourself unless you are asked.
This is especially true when it comes to discipline. Most of us were raised in a time when parental discipline was much different than it is today. We have a hard time believing that a "time out" for misbehaving is as good as a gentle swat (or at least the threat of one) on the backside. We may see this as a harmless way to instilling some much needed "behavioral adjustment", but our children have been told that it is a terrible wrong to physically punish a child, and for the most part believe it (or at least claim to). I would not argue the point one way or the other and either should you. Again, keep your advice to yourself unless asked, and even then be very careful. You may find yourself on the defensive regarding your disciplinary style as regards to them when they were growing up. If you do chose to push it, you may be surprised to find that they do not think you were very good at it.
Another area that proves to be difficult for us grandparents is the current culture that our grandchildren are living in. The almost casual acceptance of what we see as an emphasis on all things sexual can be very upsetting. We lived in a totally different culture when it came to sex. Those of us who came of age in the 50's are often shocked by what we see as totally inappropriate language, dress styles and even music. I suppose it is less difficult for the children of the 60's and 70's who are now becoming grandparents, as they are only one generation removed; but for us old pre-boomers it can be a real jolt. None the less, you are better off leaving your critical comments for times when your grandchildren are not within earshot. They do not want to hear it anymore than you did when your grandparents (and parents) expressed their horror at the sound of Jerry Lee Lewis or Bill Haley and the Comets. Remember when they would not show Elvis below the waist because his movements were considered obscene? We thought it was ridiculous and just showed how out of touch adults were. If you have done your job with your children, they are going to do the best they can to teach your grandchildren their values, which should to some extent mirror yours. If you want to instill some of your values into the lives of your grandchildren, the best thing you can do is demonstrate your values by your own behavior and attitudes.
And remember, as they grow and mature they will begin to adopt more moderate views just as generations before them did. In the meantime relax and enjoy the ride.