"Oh, yes. I was the best." she took him to headmaster office.

Pluto giggled an blushed, his messy diapee on full display in front of the headmaster.

(How about the Headmistress is an AB Kangaskhan?)

(Ok)
Headmaster, diapered Kangaskhan, smiled and walked over to them.
"Tara, how fun to see our best pupil back."
"Hi, miss Salarez. I am here because I want to enroll my little sister to your school."

Pluto shyly waved hewwo. "N-Nice to meet yoo."

"Aww, what a cutie. I will fill papers and you can take him to first class." she pinched his cheeks.
"Thank you." she said and took his new shedule. "Oh, look. Your first lesson is Baby Talk. I was good in that." she pushed stroller out of office.

"Bu....yoos no baby talking now. Why?" Pluto asked.

"I just don't like it. I was learning it but it doesn't mean it was my favourite subject." she explained. They were slowly approaching door of classroom.

Pluto shyly waved to all the caretakers an other babies.

Every students were in highchairs with trays on which they could put notebooks. They waved to him. Teacher, gardevoir in pink diaper, smiled and placed him on paws.
"I will take you later, bye sweetie." said Tara and left.
"Well, maybe you introduce yourself?" asked teacher.

Pluto wiggled in his high chair an opened his notebook. "Hewwo. My name Pluto an this my first baby class."