Mary was helping him grow in holiness. I don’t see her as being stern and saying, “You’ll go to heaven but ONLY if you pray lots of rosaries” but rather just gently encouraging him. “Yes, some day you’ll go to heaven, but meanwhile you’ll have to pray a lot of rosaries on earth before it’s time for that!”
It’s important to note that the kids were all basically “good kids”, and that as they had been taught to do, they already prayed the rosary every day, albeit rather haphazardly as kids do, trying to get done quickly so they could get back to playing. They weren’t being asked to do something they weren’t already doing, they were just being invited to step up their prayer game, and they did. Francisco and the others became more zealous about praying after the visions began. Francisco became very focused on offering his prayers to comfort Jesus.
I tend to think that Francisco prayed the rosary for the benefit of other souls in need of prayers rather than for himself.
This is correct. The children were instructed to pray for 3 intentions: 1) to save sinners, 2) for the Holy Father, and 3) to console the hearts of Jesus and Mary. Francisco particularly focused on the third intention and especially with respect to Jesus. I’m not sure where people are getting the idea that the kids were told to pray the rosary because they were too sinful to go to heaven otherwise - that’s not supported by anything I ever heard or read. The prayers and penances the children did were for others and for the world, not for themselves.
Is getting to heaven harder than I imagine?!
It’s actually not that hard if you live a good life and trust in God’s Mercy, but that’s a topic for another thread.
As discussed above, Mary did not ask the children to pray in order to make themselves more worthy of Heaven. Fatima wasn’t about the children’s salvation.