I was in a similar position to you OP. DD3 said when she was 3 years old that she wanted to work in animal rescue on land and sea. She's a teen now and wants to be vet nurse/dog handler. She wanted a dog sooo badly and for sooo long that in the end I wanted one myself.
Rescues were sceptical. Some said your youngest is too young. No way.
RSPCA said, "You can't have a dog because you have never had a dog."
Like MsGee, we took some time getting ready and more confident by walking a neighbour's dog when neighbour was having chemo and by dog sitting friends dog in our home including overnight.
We've had 2 whippets for 18 months. They came to us when they were 6. They are lovely and we all love them. The teens will walk them but not without being nagged/reminded. Only I fight with getting the dog hair and smell out of carpets and sofas, keeping the floors mud free and washing dog beds. And whippets are not big shedders, or mud magnets or smelly. Most dog breeds require much more cleaning up after.
Boychilywhippet is nervous and reactive and barks at other dogs, unpredictably. He really hates friendly young labs and spaniels jumping at him. It all needs careful handling on walks in terms of where we walk, managing him, putting him back on lead if a dog is on horizon and talking to other owners. This means my 10 year old cannot walk the dogs.
If a dog in rescue has had bad experiences or not been socialised properly then they might struggle too.
I'm not saying don't do it but I am saying don't do it without taking your time, getting experience, waiting until your youngest is older unless you can be sure you can always manage to supervise, young animals, both dogs and human can be very unpredictable.