I have read somewhere that if you used birth control at the beginning of marriage that your marriage would be invalid because the intention to delay children. Is this true?
A couple entering into marriage must be open to having children in order for the marriage to be valid (canon 1101 §2). Contraception, while sinful, is a temporary matter. As long as the couple is open to children during the marriage then the marriage is valid. The temporary sin of contraception does not invalidate the marriage.