Memories start with kun — when: Kun olin lapsi, asuin Bostonissa. — When I was a child, I lived in Boston.

Even shorter: lapsena — as a child: Lapsena asuin Bostonissa. The -na / -nä ending means as or in the role of. You already know it from the days of the week: maanantaina — on Monday.

Finnish	English
lapsuus	childhood — lapsuuteni (my childhood)
muisto	memory
leikkiä	to play (children's games)
onkia	to fish with a rod
viettää	to spend (time)
muuttaa	to move (house, country)