«You'll have to support him some since he's probably not sitting unassisted yet, but he probably has good head and trunk control.» (romper.com)
It is usually recommended that babies should be able to sit unassisted before introducing them to solid foods. (homemade-baby-food-recipes.com)
My 5.5 month old can not sit unassisted yet and hates tummy time even though I have tried all the suggestions to make it less miserable for him. (mamaot.com)