The house I bought in 1990 has no title deed. What should we do now if the original owner's child wants it back?

Although this is troublesome, don't panic. First of all, it is necessary to determine whether you are a member of a rural collective organization, which determines whether you are eligible to buy, because farmhouse members outside the collective organization cannot buy. If you don't have the right to buy, the house should be returned, but you have the right to claim compensation for the economic losses caused to you. If you are qualified to buy, you should try to prove the fact of buying, including neighbors, not to mention that you have used it for so many years, which is the best proof. If it cannot be proved, the house is given to the other party, but the other party is required to compensate for the loss.