Pull-ups (training pants) are the product parents reach for at the wrong moment and the wrong moment at the right time. Here is how to tell which you are in, and how to size them.
When to actually switch
The honest trigger is not a birthday or a potty-training book. It is the moment a taped diaper change becomes a wrestling match with a toddler who can walk, squat, and object loudly. If your kid will lie down for a change, a taped diaper still fits better, holds more, and is usually cheaper per change. Switch to pull-ups when the change itself is the problem, or when your toddler is genuinely starting to want to pull their own down.
How to size them
Pull-ups are sized by weight exactly like diapers, and the same brand-cut logic applies: a chunky toddler may need a size up from the printed range for comfort around the waist and legs. Use the cross-brand chart and the size finder for the starting number, then check the fit: the waistband should not leave a mark, and you should be able to get two fingers under it. There are no tabs to fine-tune, so the size has to be right.
Why they leak more at first
Two reasons, both normal. A pull-up holds less liquid than a taped diaper of the same size, and it has one elastic waist instead of adjustable tabs, so it seals less precisely on a moving toddler. Expect more accidents in the first weeks while you find the size and your child finds their rhythm. If the leaks are constant, it is usually the size, or the fact that a taped diaper simply fits your particular child better for now.
Overnight is a different product
Daytime pull-ups are not built for eight hours of sleep. If your toddler still needs night protection, the dedicated bedwetting pants are a separate, more absorbent line made for exactly that, and using a daytime pull-up at night is a common reason for a soaked bed. Keep the daytime ones for the day and the overnight ones for the crib.
Pull-ups are not a one-way door
Plenty of families try pull-ups, find the leaks worse and the cost higher, and go back to taped diapers for a while, then try again closer to actual potty training. That is a normal loop, not a failure. The right product is the one that fits your toddler and your week, not the one that looks most grown-up.