I designed these bottle holders as I want to be able to carry the bottles with one finger, rather than having to use a full hand. When carrying a child, hands are somehow in short supply.
I printed these in Colorfabb XT as it is FDA food contact approved, but obviously this is only as good as your nozzle and printer ...
The 2 versions are for the 4 oz and 8 oz bottle. You may want to print one sample to check the fit of the bottle, the larger one works better for me by scaling x and y to 101% ... your mileage may vary.