Are you planning on taking any lessons or just trying to teach the kids yourself?
IMHO the best option for you would be to go to Glenshee. Its the closest resort to Perth and it will have all the hills that you need.
Best to hire equipment on the way up rather than at the resort as the queues will be very long. There is a good hire shop at Bridge of Cally. BTW do not bother getting any ski poles for the kids. They won’t need them if they are just starting out. You should be able to get them into a basic snow plough without using poles. The pole will just be a faff and get in the way.
The best place to take them is the trainer tow area. This is on the same side at the ticket office/cafe about 100 meters north (towards Braemar). This is gently sloping and very wide.
Don’t bother with a lift pass to begin with as you can basically kick the skis off and walk back up the gentle beginners area. The beginners tow is a poma which requires the basic ability to stand up on skis. If its the kids first time they will struggle with this – therefore best save some money an avoid the lift. If all goes well you will have the option of buying an afternoon ticket. The only possible issue with that is that they sometimes stop selling tickets once the capacity of the resort has been reached.
The road up to Glenshee is a bit twisted and up and down after Blairgowrie. If your kids don;t travel well then a couple of sick bags might be needed.
Have fun :o)