I of course found minimal info on it pertaining to pets, but plenty in the use of humans. What it comes down to is its safe in small quantities. Its toxic by nature, but beneficial also. What it contains that is so dangerous is Atropine. So small quantites and you are ok. Although if the babies were to have a reaction I would think it happene by now, I will still cut them back. Instead of every 4-5hrs I will give it 3-4 times a day to be safe. It seems quite widely used. I did find it on a pet site for sale with this description...

Belladonna is derived from the plant, Deadly Nightshade and is a perfect example of how Homeopathy ues poisonous ingredients in minute quantities in order to cure. In its homeopathic form Belladonna is completely safe and non toxic even for young animals and for pregnant or lactating females.Can be used for blood pressure and fevers and complaints associated with hot, red skin.

Also available in liquid, cream and as a demister .

Dosage: administer a few drops by mouth three times daily or as required. Safe for use in pregnancy and lactation. No interactions with conventional medication. Homeopathics are very safe to use, please follow our guidelines however you can not over administer easily.Safe for use in eye area.
It appears it also is used in some cold medicines as it has a pseudoephedrine type of quality.

So its something to be careful with, but can be safe if used properly.