Answer:

ageone

Answer	Crossword Clue
AGEONE	Tot's milestone
AGEONE	Toddlers' parents celebrate it
AGEONE	Early birthday milestone

AGEONE	Very young
AGEONE	Early toddlerhood
AGEONE	Time of first steps, often
AGEONE	Time to start walking, maybe
AGEONE	When preliminary steps are taken?
AGEONE	When many start walking
AGEONE	Early milestone
AGEONE	When many get measles vaccines

AGEONE	What precedes a terrible period?
AGEONE	Time to start walking