Further, if the mortgage has a due-on-sale clause, if you transferred ownership to your son and daughter-in-law, you'd be in violation of the clause. Thus, technically, the bank could demand immediate payment of the entire mortgage. That's not too likely in today's market, but you should be aware of the possibility.
If you're doing it for estate planning purposes, don't do it without first checking with an estate planning attorney. There usually are better ways to transfer ownership (generally using a trust).
In any case, check with an attorney before doing anything.
Hope that helps.
It appears that your name would also be on the deed if you are on the mortgage, so it sounds like you are adding them to the deed so that they can refinance to property out of your name at some point in the future. This is common, if this is the situation. Their name on the deed gives them joint ownership in the property in the event that something were to happen to you, but it also makes for an easier transition if they are going to refinance from you at some point in the future.