Albert Barnes Commentary Exodus 22:29-30

"Thou shalt not delay to offer of thy harvest, and of the outflow of thy presses. The first-born of thy sons shalt thou give unto me. Likewise shalt thou do with thine oxen, [and] with thy sheep: seven days it shall be with its dam; on the eighth day thou shalt give it me." — Exodus 22:29-30 (ASV)

The offering of firstfruits appears to have been a custom of ancient times and was connected with the earliest acts of sacrifice. See Genesis 4:3-4. The references to it here and in Exodus 23:19 had probably been handed down from patriarchal times. The specific law relating to the firstborn of living creatures was brought out in a strong light in connection with the deliverance from Egypt (Exodus 13:2, Exodus 13:12–13; Leviticus 22:27; Deuteronomy 26:2–11; Nehemiah 10:35).

The first of your ripe fruits, and of your liquors - See the margin. The rendering of our King James Bible is a paraphrase.