Check out the local YMCA's afterschool program in your area and then undercut them by 10 or 20 percent, OR increase the cost by 10 or 20 percent.
((In our area 2.5 hours of afterschool care 5 days a week is $1700 per 12 week session... or $141 per child per week. Does not include half days ($50 per half day), no school days ($100 per day), or before school care.))
Your local YMCA will have pretty much the lowest prices in town for quality childcare. So they're a good baseline.
Another thing (or 3) to consider/ work out with the family:
- What do you do on days where you (or your child) is sick as a dog?
- What do you do on days where the 9yo is sick?
- Is this including the school's half days?
- Food
- Days where your child has afterschool activities can you be transporting the 9yo with you as you take your own child to their activities?
- Are they also asking you to take their child to any afterschool activities?
- Homework... as in are you going to be held responsible that it's completed?