When they swim with the ball in the mouth...

Guys,

Niko is learning how to swim and I realized that when he has something in his mouth (like the ball) he starts making this noise... its like a cough... like if he is swelling water. When he has the mouth empty is ok though.

Any experience on that? Is this something to be concerned about? Is this because of the format of their mouths or is this a lack of technique from Niko?

Please take a look and share your thoughts in case you have some of your experience that can help me on the matter.

Thanks,

Helder