(a) he or she engages in two or more acts of sexual conduct with a child less than eleven years old; or
(b) he or she, being eighteen years old or more, engages in two or more acts of sexual conduct with a child less than thirteen years old. 2. A person may not be subsequently prosecuted for any other sexual offense involving the same victim unless the other charged offense occurred outside the time period charged under this section. Course of sexual conduct against a child in the second degree is a class D felony.