The child almost definitely will be good at maths, but we can by no means conclude from that heritability of intelligence or of mathematical ability. The fact that his/her parents are likely to spend more time helping their child with maths and in a complex way, due to their education, confounds the issue; as does the fact that there are likely to be maths books around the house, that the parents are likely to talk about maths in a much more positive fashion than most parents would and that they are likely to have careers in maths.
Personally, I believe that intelligence is, by and large, not biologically based (except in the sense that one has to be a human without significant disability) and haven't seen any serious evidence to persuade me otherwise. I scored on 142 on a MENSA test (I believe they used the Stanford-Binet test), but I'm not sure that my parents would score as high (due to having different life experiences) and I'm not at all sure that I would have scored as high had I taken the test at other times in my life. I don't even like the concept of a "reaction range" (i.e. our genes predispose us to a certain IQ range, but that the actual range developed is related to experience) since that just seems like sloppy revisionism; I mean, obviously it's true in a very general and loose sense, but it doesn't really add anything scientifically to the debate.
(You might also like to see the videos in my signature, which happen to have some relevance.)
EDIT: Besides, there's certainly nothing like 100% heritability of intelligence (however defined) from one's parents -- the Flynn effect (i.e. the empirical increase in average global IQ scores over time) couldn't occur if there were.