Rxjs nested subscribe with multiple inner subscriptions

I'm trying to figure a way how to avoid the nested subscriptions anti-pattern in the following scenario:

parent$
    .pipe(takeUntil(onDestroy$))
    .subscribe((parentResult) => {
        child1$
            .pipe(takeUntil(onDestroy$))
            .subscribe(child1Result => child1Handler(parentResult, child1Result));
        child2$
            .pipe(takeUntil(onDestroy$))
            .subscribe(child2Result => child2Handler(parentResult, child2Result));
        child3$
            .pipe(takeUntil(onDestroy$))
            .subscribe(child3Result => child3Handler(parentResult, child3Result));
    });

What would be the correct 'RxJS way' to do this?