Page count tells you nothing. The middle page tells you plenty
Almost every picture book you pick up is 32 pages, and that has nothing to do with children. Printers fold a sheet into a 16 page signature, two signatures make 32, and any other number wastes paper. The rare exceptions run 24, 40 or 48, all multiples of eight. So the thickness is the same at two and at eight. What changes is how much text sits on each page. Open it near the middle and look at one page. One short line is a two year old's book. Two or three sentences is four to six. A full paragraph is six to eight. Most of the page covered in text is eight to ten. Do that before the blurb. Hard words you can adjust as you go, by swapping one out or stopping to explain what a boom gate is. You cannot shorten a book after a child has decided they are finished.
Two to four: the same book, again
At this age the sound is the story. Rhyme, a line that comes back on every page, a noise the child can make with their mouth. Expect the same book every night for six weeks. That is ordinary. The fact that they now say the last word before you get to it is the whole appeal. What helps is giving them a job. "You do the dog." "You turn it when the bin goes over." A two year old with a job is a two year old still there at the end.
Four to six: something goes wrong and is fixed before the last page
Around four, children start wanting something to happen. Not much. Something is lost, something goes a bit wrong, and it is sorted out by the end. The fix should land in a sentence you say out loud, not be implied by a picture of everyone smiling. A four year old asking "but did he find it" at 8.15 pm is awake for another twenty minutes. Leave the open endings for later, when they can enjoy the hanging.
Six to eight: let the character fix it themselves
By six or seven, a child wants a real problem, and wants the character to solve it. Not a parent arriving on the last page to sort it out. There is usually room for the first attempt to fail, which is the part they like. They also notice when an ending has been handed over rather than earned. If it is too easy, they will tell you. Good sentence to have ready: "What would you have tried first?" You do not need an answer. Half the time they tell you what they would have done instead, which is better than an answer.
Eight to ten: leave one page where it has not been fixed yet
At eight to ten there is space for the book to be about something. Fairness. A person who is wrong for reasons that make sense. A decision with a cost, where the cheaper option was right there. The change is that they can sit with a page where it has gone wrong and stays wrong before it turns. Younger children want that gap closed straight away. A nine year old will hold it, and the holding is where the interest is. Resist reassuring them across the gap. "I do not know either. What do you reckon?" is a fair answer, and often the good part of the night.
Reading younger than their age is fine, and very common
A nine year old who asks for the short one about the dog under the Hills hoist is not going backwards. Tired children read down. So do unsettled ones. First week in a new house, first week of a changed roster, first week back at a school where the magpies have started. For a sense of how loose these bands are: the Australian Library and Information Association reported 2,204,658 registered participants across 16,632 locations for National Simultaneous Storytime in 2025, all reading The Truck Cat by Deborah Frenkel on one day in May. Toddlers, high schoolers and adults, same book. The time to nudge upward is when a child is finishing books faster than you can open them. Try one band up, on a night when they are fresh, then let them choose the next one.
Two children, one book, and reading it down a phone
With two children on the call, or two on the couch, pick the older band and give the younger one a job. Turning is the good job. Spotting the same small thing on every page is the other one. Reading the four year old's short one first and letting them wander off after it is allowed. Video changes the practicalities more than the choice. Whoever holds the phone ends up showing their face while the book faces the wrong way, and the child cannot see the page. Propping the phone against something at their end, so both your hands are free, fixes more of that than people expect. The page problem is what we built StoryLink around: both ends see the same page, one person turns it and it turns on the other screen, and you can still see each other. The story calls and the library are free, and the books are drawn for Australian kids, which is why there is one about bin night with Pop. Whichever shelf you are choosing from, the test is the same. Open the middle page, count the lines, then read the last line first. If the last line does the work, the rest usually will.