[thesharkboy]

...two babies, believed to be at least 70 years old

I know that people are maturing later these days, but this is ridiculous.

[rimtop56]

An investigation is under way after the skeletal remains of two babies, believed to be at least 70 years old, were found ...

I believe that since the author put a comma after "babies," what is at least 70 years old are the remains. If the author had omitted the comma, then it would have read, as you thought, that the babies were 70 years old. So, I think the sentence reads correctly.