Where does “lastentajuinen” come from?

lastentajuinen (Finnish) comes from Finnish tajuinen, from Finnish taju, from Finnish -u, from Proto-Finnic -u — Forms nouns from adjectives, nouns.

Ancestry of “lastentajuinen”, step by step

lastentajuinen traces back through two separate lines of ancestry.

via Finnish tajuinen

StepLanguageWordMeaning
1Finnishtajuinenconscious; used mostly as head in compound terms
2Finnishtajuconsciousness; sense
3Finnish-uForms nouns from verbs. Most common with "e"- and...
4Proto-Finnic-uForms nouns from adjectives, nouns

via Finnish lapsi

StepLanguageWordMeaning
1Finnishlapsichild
2Proto-Finniclapcichild
3Proto-Uraliclëpćecradle
Every word from Proto-Finnic -u →Every word from Finnish -u →Every word from Finnish taju →