The XL Coffee Mug climbing hold is quite large at 7" wide. It is an excellent choice for your child on vertical walls. The incut is 1" deep and has room for two adult hands.
What's interesting about this shape is that it is a hold for adults too. The lip has a very short double incut that you can get the tip of your finger pads behind. This lip matters when the angle of the climbing wall it is set on is steep. In a roof, it offers a 1/2" edge which is an expert-level crimp.
Continuing with why it is a superb shape for the adult, it is challenging to get a thumb-catch when set on a steep wall because the bottom of the cup is 4" from the lip. That is wide for any pinch. It is a crimp in the traditional orientation and a side-pull when the handle is directly up or down.
This is the kind of climbing hold that makes you wish your local coffee shop had a climbing wall. But since it doesn't, and you do have a climbing wall, it's time to give your wall a perk.