Lambs are usually born in the spring. The warmer weather is easier on them when they are out and about.
Every ewe knows her child and every child knows his/her mother.
People wouldn’t be able to tell what lamb belonged to what ewe in a large flock.

Except for one, the pictures are from Wikimedia Commons.

Marigold and her lambs  by, sheepishly. The lambs are two days old.

320px-Marigold_and_lambs sheepishly WCA lamb taking the first steps  by, Peter Shanks from Lithgow, Australia.

640px-Lamb_first_steps_(edited) Peter Shanks from Lithgow Austrailia WCBy Dirk Ingo Franke.

320px-Friedrichsgabekoog_drei_lemmata_01.04.2012_15-11-40 Dirk Ingo Franke WCBy, anca tibor.

Touristen,_schon_wieder anca tibor WCBy, Dirk Ingo Franke.

Friedrichsgabekoog_schafe_haus_windraeder_01.04.2012_15-11-09 Dirk Ingo Franke WCeThis last picture is of a Dall sheep and lamb  by, Jon Nicholas, US Forest Service.

Dall_sheep_ewe_and_lamb_lying_down jon Nichols USFS