Hey that's a good start and a good iread to train figure drawings.
Without details it's normal that doesn't look like a children, the exercice you did here is a sketch exercice, the goal of this exercice is to understand the line of action of the model, and its general pose, if you like thix exercice you should try to go with more curvy lines, with all your arm if you can, to get a really smooth lines and shape, but TAKE YOUR TIME, don't rush this process ! take the time to observe the model and his lines of action, the way is body is.
To awnser your question, to make your drawings more look like a children, some tricks work well, like cruvy and smooth lines, really round shapes, the head should be larger in proportion to the body than an adult.
keep working you did good job bye !
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