Here is the DE Code on supervision of underage minors as contained in Title 4, Section 904. This would be the criminal aspect.
(c) Whoever purchases, buys or gives alcoholic liquor for or to a person under the age of 21 years or knowingly allows a person under his or her supervision and under the age of 21 years to consume alcoholic liquor shall, in addition to the payment of costs, be fined for the first offense, not less than $100 nor more than $500, and may be ordered by the court to perform community service for a period of 40 hours in such form and on such terms as the court shall deem appropriate under the circumstances and may be imprisoned for not more than 30 days; and for each subsequent like offense, shall be fined not less than $500 nor more than $1,000 and may be ordered by the court to perform community service for a period of 80 hours in such form and on such terms as the court shall deem appropriate under the circumstances and may be imprisoned for not more than 60 days. This subsection shall not apply to religious services or members of the same family within the private home of any of said members.
The civil aspect would be that parents are entrusting their children into your care and supervision. Therefore, if something injurious happens to a child you could be sued.
I know you said the kids could be doing outside your home and therefore, you might not have the "knowledge" that it is occuring. But if the children are coming into your home, you have a responsibility to know and to either call their parents or the police.
Congratulations to your daughter on her birthday and graduation. Best of success to all of you for the future,
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