The vast majority of Starmer's interview was about economic stability and reform. I imagine the way we support families and children could well be part of that reform.
Who is to say that we need child benefit as it is currently awarded, in this day and age? As an example, it may be better to reform, for instance, free school meals, child care etc.
We now have a majority of households with two working adults, not one. We have people, where they can, controlling the number of children they have. This has actually meant a drop in the birth rate. These things need to be taken into account.
Although Keir Starmer said he wouldn't change the two-child limit, he didn't say what he would do. I doubt he will say that before the next election has been announced. I would imagine that any such policy will be laid out in the manifesto.