My LA suggest costing TA support at £653.60 per weekly TA hour annually (38 weeks)
So 1 hour a week is £653.60; with 4 children that’s divided by 4 for a per head cost. If it’s only for 12 weeks, divide by 38 and multiply by 12 to get a 12 week cost. In reality NONE of the current grades actually costs this figure!
You may prefer to use your actual TA hourly costs, if so don’t forget the on-costs of national insurance and employers tax and pension etc.