Lost kids phone

My 10yr old lost her phone in our house, according to Life360 GPS, that's the last place it was located before the battery died. I need to get her a new phone before school starts. I'm wondering what to do since I can't trade it in. Do I just get a new line or is there another option? I'm on the Go5G Next Military plan & she is eligible for an upgrade, but we have to trade-in the existing phone.