One-on-one activities

Can anyone here help me come up with ideas for one-on-one activities that I can do with my 3yo? She has a new sister who was born in May 2023, and she's been acting out lately. I suspect it's because she feels like she isn't getting enough undivided attention. I'm hoping that I can have family watch her sister for at least a few hours now that she's older and needing to nurse less often. We're on a pretty tight budget with two kids and one income so free or inexpensive activities would be best. I just want to do something a little more special than just playing in the park.