It started with Sam.

We made the first book privately, for our own family. Sam had been calling hippopotamuses pillowbears for almost a year. He called popcorn quockqworn. He called crocodiles ducktire. They were the funniest thing about that year.

"I have to remember this," his mother said. Out loud, in passing.

Two weeks later, on Mother's Day, we gave her a book. Sam's funny words, alphabetised, typeset like a real dictionary, in cream and coral. We called it Samspeak. The brand name Pillowbears comes directly from one of those entries.

Her reaction told us everything. Every mother says I have to remember this. The funny, weird, perfect language of a toddler is one of the great delights of parenthood, and the most universally treasured. We wanted to give it somewhere to live: a real book, made to be kept and read aloud for years.

So we made the structured version: the one any mother could write for her own child, no matter what words he or she invents. Pillowbears is for her.