Bathroom floor sealer
I imagine you're talking about the bit of splashing that can easily occur, especially when children are coming out of the bath or shower.

Someone happened to mention to me just yesterday his point of view about this.  He recommended bathroom caulk.  I've seen this in the DIY stores.  You can either get a squeeze tube and just squeeze as you go, or get the rigid cylinder that goes into a caulking gun.

After you squeeze it out, you can smooth it out with a damp finger.  (You can wear rubber gloves if you wish.)