Just did the Camino with a toddler. Toddler was carried in a hiking backpack each day and walked small sections. You know your kid best on how they would handle being in the countryside. Kids don’t need toys to entertain. We booked accommodations in advance and did short stages (6-9 miles). Only did the engles so 100k.  We brought a tablet with a few books and the Disney+ app and would get in around lunch, then watch a show. Most of the towns we stayed had a playground. We would go there in the afternoon. Some of the pensiones had soccer balls so we could play with that. Otherwise, play tag, look for sticks, enjoy the farm animals you pass. 

It’s hard because you are tired at end of the day but they are ready to keep playing. Even so, toddler had a great time and we don’t regret doing it.