Ducklings should be imprinted just after hatching- or within a day or two or three. but you can still teach them a little. Take them out one at a time and sit them on your feet and use a noise (i use 'duckduckduck' all slurred together) that they can associate with you and to learn your voice. Keep them at your feet, as soon as they move away push and shove them gently back onto your feet (or between your feet) repeat. repeat. repeat. After a dozen times or so step away and make that same noise you were all along. they should follow you- if not, scoop them up and start over.
Carry them alot, hold them a lot and offer them food often.
Ducks are quick with this sorta thing and they'll pick it up after a time or two.
As for going outside, make them some sort of run, or section off an area outside for them. Or- in a pinch, just invert a large laundry basket and put it over them and a rock on top.