Not sure what this means

[pmda]

Hi, In Orberg's LLPSI Ch XIX he has a conversation between Iulius and Aemilia about (of all things) whether she's put on weight...or whether her appetite has grown since they were married. Here's the end of the exchange:

Postremo Aemilia: "Certe plus edo quam solebam" inquit, "sed nec plus nec minus quam opus est. Nimis stultus vir es, Iuli! Nonne intellegis non modo amorem nostrum, sed etiam familiam tempore augeri? Num opus est me plus dicere?"

I have translated the last part ('Nonne intellegis...' as 'Don't you know that not only our love but also our family has grown larger since then? ) But I think I'm guessing. Why is tempore in ablative? Is it because it means 'since that time'? And why is 'augeri' in passive infinitive? I'm a bit lost on that point.

[Alatius]

I presume at least that "tempore" should be understood as "with time", "as time goes by".

'Augeri' is a present infinitive, not perfect (which would have been "auxisse"), so "is growing", not "has grown". Why passive? Augeo is usually transitive, so a literal translation would be "is becoming enlarged". (Instead of "augeri", Ørberg could have written "crescere", which is intransitive.)

[pmda]

Alatius, many thanks..