My guess.... from age 7 on wards (no daycare)
EACH KID, for 10 years
$100 per month per child for activities / incidentals.. assuming only one activity at a time. (Teens work for extra clothes / activities/ school fees spending money once they are 14 or 15)
$150 per month for food (averaged!) -- higher if you succumb to packaged foods (pizza pop junk) for teenager boys after school
$60/mo clothing / haircuts / medical, other incidentals etc. --->Handme down clothes work great, but I tended to buy a LOT of second hand snow / rain wear and shoes, especially in Calgary. Lots and lots and lots of of shoes $$$ and they are hard to get second hand after age 7. Includes incidental medical / dental co pays, asthma meds or normal medical bits and pieces.
$50/mo - extra utilities, internet (because minecraft uses up all your access), $$ towards laptop / hardware access, toss in extra fuel for running around too.
$40/mo -- gift fund (for presents for your own kid for christmas / birthday, as there is only a modest amount of spend indicated above)
Monthly -- $390/month per kid over 7 years...
$47,000 over 10 years
PLUS
Saving for post secondary tuition -- $6000 per post secondary year (in 2016) x 4 yrs, increasing by 2% per year from today.
Extra $'s for family vacations. $8000 (yes, really! even camping gear costs money, mix in occasional flight..?)
Extra $'s are needed from time to time -- kids beds, desks, new fridge or washing machine, bedding, etc...Averaged over 18 years it is not so much, but it does come in mighty uncomfortable lumps. $2000
Extra for teenagers -- increased car insurance, driving lessons, grad dress, etc. $2000
Extra $'s for braces, vision / glasses or physio therapy or educational tutors or what not. -- $5000 per lifetime
Total lifetime "lumps": $41,000 age 8-18
plus of course whatever the costs through age 7 are (childcare is yikes, but the other costs can be modest) e.g., $1k/month x 12 months x 7 years = $84k...?? all in.
New total with fuzzy math: $172k per kid, age 0-17; including up to $1k/month of childcare through age 7.
--> $172k = $47k + $41k +$84k
I would say this is on the lower side --most around us seem to be spending more... remove $24k if you don't fund tuition....