“all have sinned” means every soul is subject to original sin. Children before the age of reason, about 7, can’t sin. Adults who have a severe case of mental retardation can’t sin. The Church believes God spared His Mother from original sin in order to prepare a worthy vessel, a spotless tabernacle to house the Son of God, the New Ark of the Covenant.
Then the church is wrong. Mary even admitted she needed a Savior. When the Bible says “all” have sinned that means Mary, too. No where does it say she was exempt.
Put another toddler in a room with a child playing by himself and see how long before one or the other wants the toy the other has. Nobody had to teach this little fellow to have a kissy fit...but they both have to be "taught" to share.
And here...this little gal is about to let go of the ball...and he's certainly going for it
Human nature is "sinful" from birth onward...it simply reveals itself as the aging process shows.
These fellows aren't taught to do this...they do so quite naturally