What can we learn from these? Why didn't the children get kidnapped?
From an earlier post Girl escapes attempted abduction in Calgary Alberta we find out what the little girl did and what the kidnapper did too
"...a man got out of his vehicle and grabbed the nine-year-old from behind — lifting her off the ground." "...The girl kicked and screamed until the man dropped her."
In this situation, the girl kicked and screamed. The kidnapper dropped the girl and took off.
Have you ever tried to pick up a child having a tantrum and kicking? It's difficult if not impossible. As the child is kicking they often (more often than not) will kick the person that is trying to pick them up. Now if you're a man trying to pick up a kicking child, there is a good chance that the child will kick you in a very sensitive area of your body.
As a child is moving around in your hands it's difficult to keep them in your hands/arms due to the movement.
2) Why did the man take off and not stay around and try to kidnap the other child?
The one thing that a kidnapper is depending on is anonymity, when attempting their crime. At this point after screaming the kidnapper would believe that other people maybe looking in the direction of the screaming (near by neighbors). The privacy of the crime is no longer private but very public.
He didn't try to take the other child due to the public display of screaming as well as the child that he dropped would be able to ID the criminal---which they did (please look at the link and if you have any information about this person, please contact the police)