My sister rarely sees her nephews

My sister and her husband seem to only see them on holidays and birthdays. I brought it up before how she should come see them more because they're not gonna be little forever. They're 2 and 6 months old. She said thanks for telling her and giving her a reality check. She saw them about every other weekend, then stopped doing that. We always have to initiate seeing them. This has gotten downright upsetting now. Oh, and she's 25 minutes away.

( Questions answered here as this is anonymous. )