How much to charge for babysitting

So I was babysitting a 3 year old for $65 a day 3 days a week about 6-8 hours a day. So about $8-$10 an hour. It’s in my home since I have 2 little ones and I was providing meals.

So I got paid 200 a week.

Well the parents that i babysit for had another little one and have asked me to watch him as well. And I’m just trying to figure out what to charge to be fair. I was thinking about asking for 300 a week but I just don’t know if that’s asking too much. The 3 year old will be in preschool one day but I’m assuming I’ll still have the baby that day and then both of them the other 2 days.. thoughts/opinions?