That is dangerous practice to let them breathe off your octo and I personally don't recommend you continue to let them do that. An Air embolism can occur in as little as 4' of water if she were to hold her breath. So just because it's in a pool doesn't necessarily make it safe without proper instruction first.
PADI offers the Bubble Maker course to 8 year olds, but it is not a certification. here are some details:
The PADI Bubblemaker program is for boys and girls age 8 and above. It’s fun, easy and safe. The PADI Bubble maker program is a way for youngsters to join in the family fun of scuba diving or even start a trend! Children should be OK in the water, but they don’t have to be super swimmers since the maximum depth is only 2m/6 ft.
* For children eight years and older who want to have fun in the pool
* Also available as an open water experience (two metre/six foot max. depth)
* Conducted by PADI Instructors
* No pre-training required
* Uses equipment made for children – not adults
* Typical sessions last about an hour (sign up, gear up and fun included)
When she turns 10 she can become an Jr Open Water diver:
If you are between 10 and 14 or have a child between these ages, there is a PADI Junior Open Water Diver program available.
* A PADI Jr Open Water Diver between the ages of 10 and 11 years may only dive with a PADI Professional, a certified parent or certified guardian to a maximum depth of 12 metres/40 feet.