I created three sets of verb cards for junior high school students to use. Each card has a cartoon of an action on the front, and the back has the verb in four different forms: present, present participle, past, and past participle.
Take the above picture. It is on the front of a card, and the back of the card reads:
sleep sleeping slept slept
There are three sets of twenty cards each. All of the images were created by 3dman_eu on Pixabay, a Public Domain clipart site. The raw images I used are on dperkins.org. These flashcards are A3 size, which is suitable for a classroom with 30 students, but you can resize them as desired.