I do not rely on activity books to teach S, nor do I give him many, but for me they still serve a supplemental purpose because S enjoys them. Here are two ways a toddler/young preschooler can still answer "worksheet" questions:
1. Use dot markers for selecting choices. It's hard to see in the pic, but S used an orange dot marker to choose the matching pictures instead of circling the answer (this was completed when he was about 24 months, but he started using dot markers around 18 months).
2. Write answers on small sticky notes and let your toddler or preschooler match the sticky note with the correct answer on the page. This is a favorite of S's because he loves stickers. You can also cut large sticky notes to make small ones or cut up white mailing labels to make your own "stickers".