I am a mother of three children. If I want to voluntarily send two children to a boarding school..

If you mean an orphanage, children whose parents were forcibly deprived of their parental rights are placed in the orphanage in accordance with Articles 5 and 6 of the Law "On ensuring organizational and legal conditions for the social protection of orphans and children deprived of parental care". This means that there must be a court decision on deprivation of parental rights.

Therefore, if you are deprived of parental rights, you will not be able to take care of the third child. You will be able to do this only after renewing parental rights.