It is quite unfortunate that such a thing could happen. Well, I am not surprised to hearing such a news because what ever thing of such nature involving an addict can be true as gamblers that are addicted can go to any length to do whatever pleasese them so as to satisfy their gambling urge.
In this case, this grandpa made a big mistake of his life because his granddaughter would never forgive him for doing such to her just to put his children on pressure as to release funds for him for gambling.
At this point, he needs rehabilitation so as to curtail his gambling addiction. Possibly his children had discovered that he is addicted and might have tried stoping him and might also have cut or stopped his allowance which must have prompted him from committing such crime of kidnapping his grand child and using her as a bait to get at his child to send him money so he could continue with his gambling lifestyle.
I think sentencing him to prison can not only be the solution to this situation but while serving his prison terms, he should undergo rehabilitation or transformation so as to enable him to away his gambling addiction lifestyle. I believe this could help better and also if it is possible to have such as a law it could be of good help.