• Jill Duggar shared on Instagram photos from 6-year-old son Israel David's first day of first grade
  • One snap showed Israel walking to school with the family's rescue dog, Fenna
  • Duggar said her youngest son, Samuel, is happy that he gets to spend one-on-one time with his mom

Jill Duggar's children are growing up before her very eyes.

The "Counting On" alum took to Instagram Monday to post photos celebrating the latest milestone of her firstborn with her husband, Derick Dillard. In the first picture, their 6-year-old son Israel David grins at the camera while holding up a sign that said, "Israel's 1st Day of  1st Grade."  

"1st day of 1st grade was last week for this big guy! It's hard to believe we are already here!!" Duggar started in the caption.

Duggar and Dillard are also parents to Samuel Scott, 4. The family added another member back in March, announcing that they adopted a dog, whom they named Fenna.

Another photo she posted featured Israel with his younger brother Samuel and Fenna, and they are joined by their dad in the next shot. The fourth image showed their rescue dog accompanying Israel as he headed to school.

"Israel loved walking Fenna to school on his first day & she was super happy too, but got a little concerned after he walked inside…she stood there and kept watching for him," Duggar shared.

According to the reality TV personality, her oldest son's kindergarten teacher moved up with him to the first grade and they "couldn't be happier." Duggar added that her youngest child is enjoying their current setup.

"Sam is super happy to be getting some one-on-one time with mommy in preschool at home & on-the-go with regular library visits and fun classes they offer!" the "19 Kids and Counting" alum shared.

Duggar also encouraged her followers to share their own "back to school" experiences. 

"How is he in first grade already?! Such great pics! I love that he walked her to school," one fan commented.

"My dogs just stood and looked at the door when I came home after dropping off my son. They were like, what did you do with our boy???" another person shared.

"School starts Sept 7th for us. Looks like your little man is super excited to be going back!" a third Instagram user wrote.

Duggar and Dillard welcomed their first son on April 6, 2015. She delivered him via C-section after 60 hours of labor, People reported.

"He’s worth every contraction," she said after welcoming Israel. "Every pain that I had all this long labor. Just getting to see that little baby and hold him, everything, just well worth it."

The couple welcomed their second son, Samuel, on July 8, 2017.

The family previously starred in "Counting On," TLC's spin-off of "19 Kids and Counting," before they departed the reality show in 2017.

Jill Duggar Derick and Jill Dillard pose with baby shoes in a promo for “19 Kids and Counting.” Could the TLC couple be expecting their second child? Photo: TLC