Kittens! Squee! They remind me of Bubbles when she was a kitten. This card is from another child, so once again I won't publish what she wrote, but I will share the quote she shared with me:
Glück ist Liebe. Wer lieben kann, ist glücklich.The quote is from Herman Hesse, and translates as "Happiness is love. Someone who can love is happy." Thanks to @blauerpunto for the translation!
The sender also put some very cute matryoshka-style stickers on the back of the card in bright colours. The stamp is of a Ballonblume, a type of aster flower.