I agree with all the PPs but wanted to weigh-in with a different perspective as most everyone is discussing NEWBORN costs and things do change dramatically once your child is a toddler!
A tiny bit of background since there are a million ways to raise a child, this is just mine:
My daughters is now 2 years old and I have SAH with her since she was born. We have a huge group of friends, all SAH moms with same age kids and have been meeting up since our kids were 2 months old because we all just about went insane being at home 24/7! We live in the San Francisco, CA area and there are a TON of local zoos, children's museums and play places/cafe's at our disposal and I am fortunate enough to be able to afford to participate.
With all that said, we are very active and that's why the following expenses are what they are:
Diapers: one value box of 180 diapers per month $38
Wipes: 1/2 of a value box of 6 refills or 400 wipes per month $6
Groceries just for Emily (toddler snacks only like string cheese, yogurt, organic milk and crackers, fruits, etc. in this calculation because she eats what we do for breakfast, lunch and dinner!) per month: $56
Tumbling Class (meets once a week): $55/mo.
Gymboree Class (meets once a week): $89/mo
Zoo membership (annual is $160): $13/mo
Habitot Children's museum & Studio Grow Children's play place (we go to each once a week: $60/mo
Music Together Class (meets once a week): $175 for 3month semester or $58/mo
Toys & puzzles: $20/mo (an average on what I spent this past year)
Clothes/shoes (a brand new Winter wardrobe each October and a brand new Summer Wardrobe each April) averages out this past year to: $150/m
Once a year well-baby exam: $15 co-pay only as Insurance covers at 100% (as an infant, you will need to be seen monthly through month 9 then at 1 year, 15mo, 18mo and 2 year)
Grand total: approximately $532 per month