Suspending an avocado seed over a glass of water with toothpicks is one of the most commonly tried "grow something from your kitchen scraps" projects there is, and it's worth doing for what it actually is: a cheap, genuinely satisfying way to grow a glossy houseplant, not a reliable way to grow fruit. This site's avocado growing guide is blunt about it: grafted trees fruit in around 4 years, while seed-grown trees can take up to 10 years and often disappoint even then. Setting that expectation from the start makes the project more enjoyable, not less, since there's no real chance of disappointment later.
To start, wash the seed clean of any clinging flesh and identify which end is which: the pointed end is the top, the flatter end is the base, where roots will eventually emerge. Push three or four toothpicks into the sides of the seed at a slight downward angle, spaced evenly around it, then rest the toothpicks across the rim of a glass or jar of water so the bottom third of the seed sits submerged, pointed end up. Keep it on a warm, bright windowsill and top up or change the water every few days, both to stop it going cloudy and to keep enough oxygen reaching the submerged base.
Roots typically start appearing within 2-8 weeks, though timing varies a lot and it's genuinely normal for a seed to sit doing nothing for over a month before anything happens. It's also normal for a seed to never sprout at all; not every avocado pit is viable, and there's no way to tell in advance.
Once a shoot has grown to around 15cm tall, pinch or trim it back by about half. This feels counterintuitive after weeks of waiting, but it encourages the plant to branch out and grow bushier rather than putting all its energy into one tall, spindly stem. Once the root system looks reasonably developed, pot the seed into free-draining potting mix with the top half still exposed above the soil, and keep it in a warm, bright spot. Avocado is frost-tender at any age, so a seed-grown plant should stay indoors or somewhere sheltered through its first winter regardless of region.
The honest reality check: even with good care, most seed-grown avocados either never fruit or take the better part of a decade to do so, and the fruit that eventually comes often doesn't taste like the parent avocado it came from, since avocados don't reliably grow true from seed. If the actual goal is home-grown avocados to eat, a grafted tree from a garden centre, planted in the ground with full sun and excellent drainage, is the realistic path. But as a low-cost windowsill project, especially with kids, growing one from seed costs nothing but a toothpick and some patience, and it's a genuinely good-looking glossy indoor plant for years regardless of whether it ever fruits.
most seed-grown avocados either never fruit or take the better part of a decade to do so, and the fruit that eventually comes often doesn't taste like the parent avocado it came from