De pequeña era muy tímida y educada. Me gustaba salir fuera y leer pero no me gustaba jugar con ositos* de peluche y muñecas. 1- I'd say that "De" is the most similar word to "As a" in castilian for the context you are using it. More examples: *De adolescente me encantaba jugar al fútbol - As a teenager I loved to play soccer *De estudiante solía suspender Inglés - As a student I used to fail english 2- You are right, well behaved means "bien educada". You can also use the words that Noelia and Edgar told you, Maybe just "educada" is more appropriate in Spain and "bien educada/portada" in some Latin America countries, 3- Teddy bear means "oso de peluche" but it's better to use "osito de peluche". Colloquially, when we refer to this kind of toy, we use the diminutive "ito" which means little or smaller on the word "oso" (to make it cuter i guess) but "oso" is ok too. I hope I explained well

As a child I was very shy and well behaved. I liked to go outside and read. I did not like to play with teddy bears or dolls. Yo de niña me portaba bien y era muy tímida. Me gustaba salir a la calle y leer. No me gustaba jugar con ositos de peluche, ni muñecas.

Cuando era pequeña era muy tímida pero educada (se "es" educada o se "está" bien educada; bad quality plus good quality with "pero") . Me gustaba ir afuera y leer. No me gustaba jugar con osos de peluche o muñecas.

Cuando era una niña era muy tímida y bien portada (o como dijiste tu "bien educada"). Me gustaba ir afuera y leer. No me gustaba jugar con osos de peluche o muñecas