Have Ye Not Read?
Question: Can a man qualify to be a deacon if he has adopted children, but has none of his own? What do the Scriptures teach?
Reply: Some believe that a man cannot qualify to serve as an elder or a deacon in the local church unless his children are his natural descendants (his own flesh and blood). We agree that deacons and elders must have children (1 Tim. 3:12; Tit. 1:6). The question pertains to adopted children.
If a man adopts children, they are his children; therefore, he has children. The Greek word tekna (children) not only means flesh and blood descendants (Rom. 9:8) but, in this same verse, the word is also applied to children of promise (see also Gal. 4:28). Paul speaks of the adoption of sons (Gal. 4:5), so the word "children" is not limited to children of the flesh to the exclusion of children by adoption. If a man rules and controls his children (whether they be his flesh and blood, or whether they be adopted) he meets the qualification as to children. In either case, they are his own children.
We also need to remember that the qualification for a man to serve as a deacon or an elder, concerning children, is not dependent upon his ability to sire them but to rule them. If he is able to control and rule the children who are in his household, whether he has sired them or adopted them, he is scripturally qualified in this regard. There is no reason to suppose that the children in the family of a deacon or an elder have to be his own flesh and blood in order for him to be scripturally qualified to serve.
Guardian of Truth XXVI: 7, p. 98