4 month old kitten has diarrhea

Hi! Just after a quick bit of advice - 

One of my kittens, who is 4 months old, just had case of very loose stool. She's never had the issue before and usually has extremely normal movements, but she has just sat down at had a very noisy, very smelly one that ended up all over her back paws. (She wasn't happy that she had to have a bath!) 

We've given the kittens a quarter of a bowl of Whiskas cat milk earlier today, but she's had it before and has had no issues.

Other than this she's seemed very happy and energetic all day (though she's been extremely needy and attention seeky - more than usual) 

Is it likely that this was a one-off occurrence and nothing to worry about or should we be concerned that she's unwell? 

- It's also possible that she had a few licks of chocolate milk earlier, but that was only one or two licks before I ran over to remove her.

If it was only the one occurrence then it was likely just a reaction to too much Wiskas Cat Milk or chocolate milk. She could also be developing a higher sensitivity to lactose and the 98% reduction in the cat milk might still leave too much for her body. Whatever the reason if everything is back to normal after the one incident then you probably can just reduce the cat milk and call it a one off. Between the cat milk, possible chocolate milk and the explosive reaction I am leaning towards a lactose overload in her system that shouldn't reoccur now that it is out. 

However, if you notice she has loose stool in the litter box or any other symptoms you'll want to take her in. 

When it comes to vomit or diarrhea in kittens they can easily get dehydrated so even if it things are mostly back to normal they could be dehydrated; the vet can give SubQ fluids to re-hydrate to aide in recovery. My general rule when it comes to kitten care is anything happens I make an appointment for 24-48 hours out. If it doesn't reoccur I can cancel the appointment, but if it does reoccur I already have the appointment set up. If you do this though, communicate with the vet when you make the appointment that it is that so they can double book the time or let you know if there is a minimum cancel time. I've had times when I still take them in as kitten just to update their weight, get a quick once over, and possible antibiotics or fluids depending on how the vet reads it.