Volunteer! See a Show
Enter contests to volunteer at concerts of your nieces/nephews favorite bands. Several musicians are allowing people in the community to help with various campaigns and fundraisers and offer a ticket for a free seat at the show for doing so. As long as your niece/nephew is in the allowable age group decided by the cause, you're usually welcome to bring them along.
Search the web for opportunities such as with Oxfam or with your fav band/musicians. I did this for the Oxfam/Coldplay Make Trade Fair Campaign, brought my husband and our 15 year old niece, and had a wonderful and rewarding experience.
My niece was even able to apply the volunteer work to her National Honor Society hours of community service. Oxfam was happy to send an email to her for her school records.