What do you call the facial expression or the state just before bursting into tears?

What do you call this facial expression that forms just before bursting into tears? (Especially when a baby has been treated in a way he/she didn't expect and consider it unfair or feels neglected. Of course this pitiful and sad expression with lower lip protrusion is most commonly seen in younger kids; and is not acceptable for adults or they will be considered to react childish.)

Actually I need to know the answer to complete these sentences :

"When the father yelled angrily at the baby, he (the baby) ..(?) and then burst into tears. "

"When the mom took the toy from the baby, he ...(?) and cried."

PS: We have a phrasal verb in Farsi for describing this state and we use it for kids or adults, but when we hear it about a kid we would definitely think of a baby with this facial expression specially with the protruded lower lip. For adults, we would think of them in the state just before bursting into tears, for example; some winners react like this when they recieve their awards or when they are about to make a speech.

Note: Since I need to complete those sentences and they are about kids, if I know the term used for talking about/ referring to this kids' facial expression or state, that would solve my problem.

Solution 1:

Quiver: tremble involuntary, the action the lower lip does when a person is about to burst into tears or sob loudly.

• His lower lip began to quiver, his face contorted, and the tears began.
• Tears welled from his eyes now, his lower lip quivering...
• ... her lower lip quivered, her eyes were puffy and red. She was on the brink of crying again.

Puckered: to draw together, crease, fold, and wrinkled. How a person's face appears when they can't hold back their tears.

• the child’s face puckered, ready to cry

• Speaking to the infant in a pitiful, compassionate voice, he said, “Oh! is the baby hurt? Poor thing. What did you do? Does it hurt? Show it to Mama.” Sure enough, my happy little cousin puckered up, started crying and made his way to his mother for emotional support.

• The child puckered up her mouth in an effort to stop the tears but it was useless. They flowed down her dirt streaked cheeks...

Oxford Dictionaries: pucker, quiver

Clair Danes, alias Carrie Mathison in the TV series Homeland, mastering the lower-lip quiver

Solution 2:

"When the mom took the toy from the baby, ..."

"When the father yelled angrily at the baby, ..."

his (little) face crumpled and then he burst into inconsolable tears.

Crumple - to become incurved or crushed together; to contract and shrivel up; to become creased or wrinkled by being crushed together (OED) - suggests the important (as I see it) involuntary aspect of the facial expressions in the images.

Solution 3:

The term is to pout:

• to ​push the ​lower ​lip ​forward to show you are ​annoyed, or to ​push both ​lips ​forward in a ​sexually ​attractive way:

  • Vanessa always pouts if she doesn't get what she ​wants. Caroline pouts her ​lips when she's putting on ​lipstick.

Solution 4:

Welling up.

"When the father yelled angrily at the baby ,he welled up and then burst into tears. "

"When the mom took the toy from the baby, he welled up and cried."