So you're practicing standing, but it seems difficult for the child and you can't figure out why. Or maybe they become fussy with practicing standing either in their stander or at the coffee table. There could be several reasons that standing is difficult so this post is NOT one size fits all, but have you checked range of motion? The most common areas that I see tightness is the hip flexors and hamstrings, both of which are being slightly lengthened with standing activities. Although kids do not reach full hamstring stretch or hip flexor stretch with standing, if there is some tightness, you will see the effects of it with standing. Here is a simple way to check range of motion and stretch.
In this example, the hamstring length is pretty limited and hip flexor length is slightly limited. If you notice this, it may be time to incorporate some stretching into your daily routine. Research states that we need to stretch for at least one minute for it to make a difference on a muscular level. My goal is to aim for one minute, but at LEAST to tolerance, meaning the child is not fighting back or crying.
Here is a hamstring stretch. I use my leg to keep one of his legs on the floor, and use my one hand on the knee and my other hand at the ankle to move the whole leg in a straightened position up towards the sky while keeping the other one on the floor. This stretches the proximal portion of the hamstring (the part that is closest to the booty). The second part of the video is a distal hamstring (the part closest to the knee) stretch, where you keep the hip at a 90 degree angle and bring the ankle towards the sky.
In this video, you'll see a hip flexor stretch. Lay the child on his side and use one hand to keep the hips stabilized and the bottom leg from moving. Use the other hand at the top thigh/knee area and move it back towards you.
Disclaimer: This is not a magic potion that will help the child stand with no issue. This is one part of the puzzle. There may also be coordination difficulties, abnormality in tone, decreased strength, and many other factors that are contributing. Please reach out to a PT or your pediatrician if you have concerns!