you won't really be renewing your visas- you'll be applying for a different one. Indefinite Leave to Remain, to be exact (ILR), which is a permanent visa that allows you to live and work in the UK, well, indefinitely! When you apply, you'll need to provide proof that you've been living in the same house as your British spouse/partner for the last two years, in the form of mail addressed to both of you (seperately or jointly) that covers that entire period.
There are *tons* of threads on ILR and ILR applications on this board, so you should find some if you do a search and/or dig through some old threads. Your son can be included on your application (as long as he is still under 18 when you apply), and the fee is £750 if you apply by post (more if you apply in person).
You'll also need to pass the
Life in the UK test, which is required of all ILR applicants (minor children are exempt though.)
You can apply for ILR 28 days before the 2-year anniversary of your arrival in the UK- no earlier, but of course you must apply before your visa expires.