The long ferry to Holland leaves you a fair way from France, and I’m not sure the wee one would sleep great on it. IME it’s a lot of £££ too.
I have great memories of our (then 18-24ish month) daughter standing on the bed by the window of the Dover Travelodge excitedly watching ferries come & go on the morning we sailed (took us two days from Scotland to Dover though, so I know it’s a compromise).
There are loads of great campsites all over France. Are you taking a tent, or looking at a static caravan?
BITD, we found some gites (cottages) which catered specifically for pre school kids, so there were other kids the same age, an indoor play area, etc. I think where we were has changed now though.
We’ve stayed at a few Yelloh! Sites with our own caravan more recently (and will this summer), which are great, but you won’t need kids clubs, etc yet.