This baby foot-muff pattern is designed to work with a standard 3 strap safety mechanism: 2 x shoulder & 1 x groin. However it could potentially work with some 5 strap mechanisms too as the sides are open enough to put extra straps through.

Some basic sewing is needed if you wish to line the foot-muff with fleece to keep the little one warm in winter, otherwise the knitted fabric will do just fine for cool - Springtime weather. It is possible to sew the lining on by hand but I would recommend using a sewing machine to speed up completion of the project.