The OP said a change of social life is what the family are after. I,d say with three young kids your social life at kids groups and school in future will change from the nights on p@@s your real friends still take part in.
I find yes you meet people via schools and sports clubs but you have to push your way in to their lives or invite them into yours. My child is not a team sports girl and that automatically excludes us from a lot on socialising.
Your life with kids will keep changing and so will friend groups, wherever you live.
Will ll a move to Australia fix that, big decision and you giving up a lot. You don't know what you've lost until it's gone is how I feel.