Can't comment on the Punta Tombo option but we enjoyed the Valdes Peninsula tour. Your question made me go back to my FB post to see the photos and remember exactly what we saw. We took a tour with local company Sentir Patagonia (who knows if it is still operating!). We stopped at a Interpretation Centre at the entrance to the reserve which included a complete skeleton of a Southern Right Whale and baleen plates available for us to touch and feel. Our driver kept an eye out for any wildlife along the way and we saw a Patagonian Mara. We stopped at a penguin rookery and because we were there in Dec/Jan we saw Magellanic penguins and chicks quite close. It was also the time of year when the elephant seals were moulting so we saw them lying on the beach. If I recall correctly, I think this is also the area where killer whales can be seen at times, but we didn't see any. Our final stop was at Punta Piramides where we saw sea lions with young calves. So lots of wildlife which might be of interest to a 4 yo. I think the total drive time is less for Valdes Peninsula, which might be a factor to consider, but it was still a long, boring drive. Hope this helps. Loved this cruise.