The OP describes a scenario that uses an extreme situation to try and pose an ethical dilemma for us, to dismantle our sense of right vs. wrong. But it's a trick question. Anything taken to extremes often falls outside of the normal, functional paradigm, leading to a breakdown in the model. So what. Same goes with science, like as with the quantum mechanics. No one can say for sure what they would do in such a scenario, or whether any of the 3 options actually represent a chance of success. It's a lose-lose situation.
So given the absurdity of the situation, rather than try to answer with one of the no-win scenarios I tend to ask more general questions. Let's step outside the box. How did the child get lost? How did they get involved in such a bizarre scenario? Why was there no guardian with them, or anyone from the public that would be able to see what was going on. We "find her" with a bomb attached that will go off in 5 minutes. Where? Where did we find her in that crowded mall, how did the terrorists manage to take her and attach a bomb and set up a timer, without being observed and someone intervening or calling security.
Obviously, this child ran off and was talking to strangers. Maybe even associating with bad people, as kids sometimes do these days, given they're empowered as though they are adults, to make choices about their own liberty, without having reached the age of reason.
So I say, the people who taught my kids in elementary school that they have equal rights and don't need to listen to what mommy and daddy tells them, the teachers with their social agenda, them who teach kids to be non-judgmental, because everybody's ok, they're the ones to blame for that child being strapped to the bomb.