I run a babysitting service with over 30 families, i have been a nanny and also a director in the childcare field so i have lots of experience with this!
If you go through an agency you will have pretty much gauranteed quality and security. But you will pay more vs hiring on your own.
I did lots of research on the rates when i was nannying. The avg nanny works 40-50 hours a week and makes between 12-18 an hour depending on what you want them to do. are they just watching kids? how old are the kids? laundry? teaching? cooking etc?
You best bet is to go by a salary for the week. Most nannies also get 2 weeks of vacation a year. Are you going to pay nanny taxes or no? You are required by law to pay social and medicare if they make more than $600 a year. The nanny pays federal.
There is lots to look into with this option.
But if you are doing 45-50 hours a week and expect the nanny to watch kids, cook, pick up, laundry, teach etc. than you need to go about $15 an hour. Also you are in Colleyville where most pay higher.
I can tell you my babysitting rates are $12/hr for 1 & 2 children and $2 per hour more for each additional child (4 kids $16/hr) and this is just sitting for the normal nights/weekend sittings.
Hope this helps