Please understand that no kidnapping case is available to you. The mother is also a legal custodian of the child like you and hence for upbringing if she gives the child to her parents as she may not be available to look after the child during day time, it cannot be branded as "kidnapping".
Now, two things have to be understood. You want the child near you and you do not want it to be given to any near blood relative to look after. In other words, you are telling that your wife should not go for job and she shall be a house-wife. In that process, you are curbing her fundamental right of earning some thing from doing job in the name of looking after the child. If both mututally agree for such adjustments, then it is O.K. But, for me, it does not be acceptable to your wife. She does want to earn and become self sufficient by doing some work and not dependent upon you. she does not want to be in the job of housemaker. If that is so, her desire to have a job is quite justifiable. You also may not accept that if any one asks you to leave the job and sit at home and look after the child. Same is the condition with your wife. The days have gone that a only wife has to be home maker and the husband is the bread earner.
To solve this problem, your wife suggested of giving the child to the blood relatives, i..e., her parents to look after the child. If her parents are also living in the same town, you should not object for this and evenings you can pick up your child from them and keep the child with you for the nights along with your family. If they are residing in some other town this arrangement may not be possible. Then, the better way is to have a thorough discussion with your wife and engage a whole time maid servant (eventually, she is also called nanny), which may solve your problem. If you insist that she should abandon her plan of doing job and refusing to give the child, brings the problem to square one and she would again leave you along with the two children and go to her parental home and does some work for earning. In such eventuality, you will be deprived of the companionship of both the children. If you run for the years together in the court, you may finally get "visitation rights", but the children will grow up with her maternal side grand parents, which you do not like and which your wife is suggesting right now.
Hence, do not be adamant and be flexible instead of filing criminal cases against your in-laws.