Add olive oil into the pot and sauté the garlic and onion on medium for a few minutes and then lower the heat to medium-low and add all the celery, carrots, and potatoes (if using). Sauté for a few minutes.
Add the lentils and water. Then turn the heat on to medium-high and allow the water to come to a boil. Once boiling bring the heat down to medium-low, cover the pot, and let it cook for around 45-50 minutes.
After 45-50 minutes the lentils should be soft. If not continue cooking until they are.
Once soft add salt* to taste and let it simmer for about 15 minutes
Notes
*Separate a portion for your baby before adding any salt.You may also add garlic salt and oregano to taste.TO COOK IN INSTANT POT: add all the ingredients and pressure cook on high temperature for 25 minutes, let the steam release on its own for 15-20 min and just add salt to taste. Season to taste.