My advice would be whatever you end up choosing make sure your clients are aware in writing in your policies if you are stepping outside of your home to the front of your property to retrieve children from the bus while others are in the house either asleep or quietly engaged and I would also invest in a 'video monitor' as well so that you can still SEE them while you are doing this that way they were never being left 'unsupervised' so to speak.
I cannot find the case law link online by there was a provider a few years back who stepped out to the end of her driveway to get the mail during quiet time and a child was injured during those few moments cause they climbed out of their crib ~ parents sued and she was found negligent for having left them 'unsupervised' with the courts arguing that had she be IN the house at the time of the accident she could have heard the child stirring and gone up to prevent him from climbing out .... seriously that was a very RARE set of circumstances aligning on that poor provider making her life hell ... the fact is that as 'business owners' we are held to a higher standard than 'parents' cause while we all know that parents everywhere step outside their homes ALL THE TIME with the kids inside and that kids climb out of cribs ALL the time in their homes parents do not sue themselves if their kid gets injured in that moment we on the other hand are being 'paid to provide a service' and if something happens we are on the hook of scrutiny of the public eye :(
I have a supervision policy in my parent handbook that clearly states that at times of the day I am using other senses or means to supervise children because I am but one person and my eyes cannot be directly on ALL the kids all the time so monitors and other venues are used to assist me if I have to step out of a room or nip inside for a second while they are outside and so forth.

