Window guards can easily be pried open by the FD, if chas v’sholom they need to get in. Unless you live in a basement, put the window guards on each window. Even a fall from the 1st floor 6-8 feet) can be a real trauma to a toddler, if they land head first. From the 2nd floor and higher, ask a hatzoloh member what that can mean (I don’t even want to think about it)
The horror stories you hear about are iron bars, like the ones that are all over BP. Those are a death trap. Worried about a break-in? Get insurance for $500/year. Your family’s safety is worth more than that; don’t risk the iron bars.