1.
If you ~ a piece of material, you keep it in position by placing one edge or end of it behind or under something else. For example, if you ~ your shirt, you place the bottom part of it inside your trousers or skirt.
‘Probably,’ I said, tucking in my shirt...
Tuck the sheets in firmly.
PHRASAL VERB: V P n (not pron), V n P
2.
If you tuck a child in bed or tuck them in, you make them comfortable by straightening the sheets and blankets and pushing the loose ends under the mattress.
I read Lili a story and tucked her in her own bed...
My mother would tuck me in, turn out the lights and tiptoe out.
PHRASAL VERB: V n P n, V n P