Yamato knows Onigashima layout well after living there for 20 years and where to hide. Momonosuke was also okay with hiding
Nami and Usopp doesn't. And Tama wanted to FiGHT (To Nami in 996 : We came here as samurai! 1004 : I want to go Onigashima too!)
if any, staying to fight the two ancient zoan while leaving Tama alone is even more dangerous because there's no guaranteed she would hide. She showed she was reckless by coming in the dome full of beast pirates alone.
I just completely disagree with the "Nami and Usopp used the child as a weapon". This wasn't how it the story presented at all. It was Tama's own bravery and initiative.
