And bandwidth  

 There's definitely an opportunity cost to raising children.

I'm not sure that you can quantify the return that they provide you though. So far the return has been in them forcing me to grow as a human & the odd reciprocation of love & affection. I'm betting that there are other benefits to come as they move into adulthood.

I'm hoping that they start generating their own sats soon. 

 Best to have a low time preference.  I look at fatherhood as a long term investment.