Tantric reincarnation is very strict, and there are complicated rituals, not just finding a child.
Since he is a reincarnation, he is the reincarnation of the living Buddha in his previous life. Because the living Buddha in his previous life vowed to come back and continue to save all beings, there is no possibility that he will not do this job when he grows up.
According to the argument, the reincarnation of living Buddha can also be divided into monk appearance and family appearance. A living Buddha who becomes a monk, acting according to the monk's precepts, naturally cannot get married.
However, some living buddhas are reincarnated as practitioners at home. The purpose is to set an example for laymen who practice at home and show how they practice Buddhism at home. It is also possible to show that practicing at home can be achieved. For example, there are many such yogis living buddhas in Nyingmaba (Red Sect). They can get married.