Choose variant 1 (regular) if the child doesn’t wear a diaper, and variant 2 if the child has a diaper. Variant 1 has a close fit. Variant 2 is designed to allow for room for the diaper and to be higher over the behind.
Choose a size based on the child’s height. If you know that the child is slim you can size down on width but keep the length, i.e. combining 2 sizes. If you’d like a more loose fit, you can size up 1-2 sizes on width, but keep the length.
Lo is designed for knit fabrics with at least 30% stretch. Evaluate your fabric with the help of the stretch guide in the pattern.