This was designed by someone who's never been around children.
Within the first 5 minutes, that kid is going to jump up and intentionally miss that standing bar. The most likely outcome is a new chronic back pain issue, and probably topple you over onto that kid in the bargain.
Back pain is a given, even if the child and/or halfling stands on the bar as intended. There needs to be a way to distribute the weight to one's hips, like a hiking backpack or SCBA. The shoulders and spine should be used to keep the halfling stable, and not be used to support their weight.
right, ideal use case would be a spear brace where the mount can stop any charging enemies while the halfling is in ideal position to crossbow those who get too close
In the campaign I'm in, I play a tiny Ysoki (homebrew race) and I ride on the shoulder of my minotaur friend. I get a +2 to AC and a stealth bonus, it's great