If your ex does not let you see your child and there is a divorce decree, separation decree or a court agreement that regulates a visitation regime, he would be breaking it . The problem arises when there is not yet a court ruling or agreement and one of the parents prevents the other from seeing their child.
Article 160.1 of the Civil Code states:
Minor children have the right to interact with their parents even if the latter do not exercise parental authority, unless otherwise provided by court order or by the Public Entity in the cases established in article 161.
That is, children have the right to interact with their parents. In chinese overseas europe database addition, article 90.1, section a) of the Civil Code establishes: the regulatory agreement must contain at least: (…) the communication and residence regime of the children with the parent who does not habitually live with them.
Parent-child relationships are a right and a duty.

What can I do if my ex won't let me see my son?
Well, it depends on the circumstances:
If there is a divorce or custody decree that regulates a visitation regime, or even shared custody, and the other party prevents you from seeing your child, there are two possibilities:
Go to the police , bringing the court order to prove that you are entitled to be with your child and that your ex-partner is not letting you see him. This option has the advantage of being quick as long as the police intervene and try to reason with the parents to enforce the court order or regulatory agreement.
If the situation is repeated over time, you can go to court and file a claim for non-compliance with the judgment and request its enforcement. You can also request that the delivery and collection of the minor be carried out at a Meeting Point (public place).
If there is no court ruling , you must file a divorce or custody petition and request that a visitation regime be established. The problem is that this process is slow, so it is advisable to request provisional measures in the petition so that the judge, while issuing the ruling, establishes a visitation schedule for your child and in this way you are not deprived of your right while the process comes to an end.
Can it become a crime?
A court ruling must be complied with in its entirety. If your ex-partner does not allow you to see your child, he would be violating the ruling that regulates a visitation regime.
Article 225 bis of the Criminal Code regulates the crime of child abduction and any parent who does not take the children to the non-custodial parent or takes them to a different address without consent may incur in this crime. He or she will be punished with a prison sentence of two to four years and special disqualification from the exercise of the right of parental authority for a period of four to ten years.
To answer the question we must refer to article 1902 of the Civil Code:
Anyone who, by action or omission, causes harm to another, involving fault or negligence, is obliged to repair the damage caused.
If your ex-partner does not let you see your child, you can request compensation for the damages caused. You should know that the assessment and proof of these damages are difficult to prove in most cases.
Requirements to apply:
It must be a conduct or omission that makes the development of the established visitation regime impossible.
There must be verifiable moral damage that has been caused by the deprivation of contact with the minor.
Cause-effect relationship: relationship between the custodial parent's conduct and the harm suffered by the other party.