You are approaching scrupulosity friend. Sometimes we can think way to hard about things. Maybe join a continuing ed faith group at your parish for interesting topics of discussion and a pulse on Catholic thought. Perhaps others can recommend good books on Morality as well.
One does not sin by accident. So you accidentally broke a small toy. That is not a sin.
But what are you going to do about it? You are obligated to make reparation for the damage. Failure to do this can be sinful. The sin won’t be in the breaking of the toy because it was an accident. The sin can be in the failure to perform any obligation that may arise because of it.
Even intentionally breaking a small toy is not black-and-white. Whose toy? Your kid’s? How many toys does he have? Can it be easily replaced? Perhaps venial sin.
A poor child’s whose small toy is his only joy, and you broke it solely to break his heart? Same value of toy, but could be mortal sin.
If you steal five dollars from a billionaire? Likely venial sin.
Steal the last five dollars from a homeless beggar who would have bought his supper with it? Likely mortal sin.
It’s not just the value. It’s also the circumstances the surround the sin.