For your first question, it sounds like you’re interested in tabular data on metro areas by population size. If so, I’d recommend using IPUMS NHGIS, which provides summary data for targeted geographic areas. You may be interested in this brief tutorial on using the IPUMS NHGIS data finder; I will walk through the steps for how you might find total population by MSA for reference as well. Start by clicking on the “Get Data” button. For Geographical Area you want to select “CORE BASED (METROPOLITAN/MICROPOLITAN) STATISTICAL AREA [2003-PRESENT]” and under Topics you want to select “Total Population”. To get the most recent estimates, you would select 2019 under Years and 2019 ACS under Datasets. Then choose the “Total Population” table.
I’m not sure I understand your second question. Household incomes are the sum of all individual incomes within the household. It isn’t clear to me if you are referring to households composed only of children or simply households with children. Please let me know so I can provide further guidance. However, as it sounds like you are interested in summary data, I would encourage you to check IPUMS NHGIS.
If you are looking to calculate summary statistics using the individual-level microdata in IPUMS USA, you may be interested in the online analysis tool; I am also linking to a brief tutorial on using the online analysis tool and a data training exercise that will provide a guided example of how to use the tool. Note that if you use IPUMS USA, the value labels for the numeric strings associated with specific metro codes will be applied if you read an IPUMS USA extract into a statistical software package. You may also reference the codes lists (e.g., MET2013) to update them on your own if you are not using a stats package; note that not all metropolitan areas are identified in the individual-level microdata available through IPUMS USA.