All my kiddies transition out of a high chair as soon as they are able to sit at the table safely and see over the edge with enough room to feed themselves. Its different for every child, especially for the petite ones. It does usually happen anywhere around the 18 mth mark to 2 years. I have a boy now who is nearly 18 months (couple of weeks away) and he isn't big enough to sit at the table yet. I have the ikea highchairs which stack on top of each other so take very little room up. Whether I have 1 or 4 out it doesnt make any difference. I would hate to have boosters out all the time but can understand it if this is someones only option.