We did a few Eurocamp holidays a long time ago. Did a couple of overnights in Brittany, and didn't like the campsites. Might be different now, but it felt like being in the UK. First time, we drove to SW coast and stayed in a tent. Second time mobile home and nobody wanted to go back to tents. Four year olds won't care, but you might!
When our kids were that young, we chose quieter camps. When older, they liked livelier. Also, when we first went, we couldn't afford to eat out so shopped at local supermarkets (one of the highlights). In the last couple of holidays, we made sure we were near restaurants.
I like being very close to the beach, so it's worth going just for an hour or two if it's very hot, rather than it being a car trip. Some campsite pools got very crowded. Might just have been our kids, but they never wanted to leave the campsite. They always made lots of friends (usually Dutch children).
I was very nervous driving off the ferry every time, but I soon got used to it, and I enjoyed driving around. Then we did a couple of fly drive holidays. Obviously saved the long drive, and it allowed up to go to Spain and Italy rather than France.
Our children, all grown up now, have very fond memories of those holidays.