Many children are old enough to learn short brachot (and somewhat understand them, if explained), but don't have the memory/patience for longer brachot.
Frustratingly, many of the brachot that could be introduced naturally in a child's routine are long (eg. asher yatzar, ḳiddush, birkat hamazon, aḥat me'ein shalosh). One suggestion could be using (non-Hebrew) alternative phrasing (not a bracha) that expresses the intent of the bracha (eg. "God makes all food, thank you for the food" for birkat hamazon). However, one could also teach a child a part of the "real" bracha that the child can reasonably learn; one simple option would be the ḥatimot of the long brachot (eg. בא״י הזן את הכל). Teaching part of the "real" bracha seems preferable, since the goal is eventually to teach the entire bracha, and if the child learns part of it now, learning the rest later will be easier (and make more sense to them).
I was wondering whether there is discussion as to the permissibility of teaching the ḥatima independently of the rest of the bracha. Short of learning the full bracha all at once, is this a permissible half-way step? Is there any discussion of converting the ḥatima to one with shem and malchut (ie. בא״י אמ״ה) for the purposes of saying an entire short bracha? Might the age of the child matter: older than 6 or 7 ("ḥinuch age") versus younger?
A potential source against my suggestion is the rule prohibiting turning a long bracha into a short one (ie. turning בא״י אמ״ה גוף הברכה בא״י חתימה into בא״י אמ״ה חתימה; see mBrachot 1:4 with tBrachot 1:7). From what I understand, ḥinuch should be as close to the "real thing" as possible (see 1, 2, 3, 4, etc.). Thus, I presume that adding shem and malchut to the ḥatimah is impermissible, even for ḥinuch. But perhaps just teaching the ḥatima as a half-way step is not fully making a short bracha out of a long one?
A possible argument for just using the ḥatima is the allowance of the formula "ברוך (...) מחדש חדשים" for the unlettered (see Sanhedrin 42a), instead of the full birkat halevana.