Can adults be prosecuted for providing alcohol to minors?

Yes. Providing intoxicating liquor or cereal malt beverage to a person under the age of 21 is a class B misdemeanor. The punishment is a minimum $200 fine and a maximum $1,000 fine and/or up to 6 months in jail. K.S.A. § 21-3610 (1995) and K.S.A. §21-3610a (1995)

In addition, adults may be charged with child endangerment, which is defined as intentionally and unreasonably cause or permit a child under the age of 18 to be placed in a situation in which the child’s life, body, or health may be injured or endangered. Child endangerment is a class A
misdemeanor, which means fines can be up to $2,500 and adults face up to one year in jail. K.S.A. § 21-3608 (1995)

Can a person that is 18 or over, but under 21, also be charged with these crimes if they provide alcohol to someone under 18?

Yes. In State v. Sampsel, 268 Kan. 264 (2000) the Kansas Supreme Court held that the statutory prohibition against furnishing alcoholic liquor to a minor applies to minors as well as adults.