Probiotics are fine as long as your child doesn’t have a Central venous line

There’s no reason to give probiotics to an otherwise healthy child. If they have symptoms, such as diarrhea, they need to be evaluated and then a decision on the efficacy of probiotics can be made

I am not aware of any recommendations or benefits related to probiotics in healthy children.

There is no evidence whatsoever that healthy adults or children need to take probiotics. No peer-reviewed published studies at all. Don't fall for the sales pitch from probiotic manufacturers that claim a bunch of health benefits. No proof of this. Save your money and focus on providing a your kids a healthy diet, which I imagine you are already doing.

I don't think it is advisable.

Probiotics are generally safe at any age. There is no evidence that a probiotic daily is associated with a healthier gut. However, a good diet will promote the growth of good bacteria in your gut associated with a healthier gut.

Beneficial bacteria are naturally present in the healthy gut. 4 and 6 year olds generally do not need commercially manufactured probiotics.