I'm concerned about my 15mo gross motor skills. He is a super fast crawler (everyone comments on this) and crawled at around 10 months (first army crawling and then a month later up on all fours). He can cruise easily and walks quickly using a walker (but never voluntarily uses it - we have to put him buy it and encourage him). He can climb up and down from the sofa and onto and off of beds and does this all the time. He can climb up a slide, sit down on it with his legs swung round unaided. I know these are encouraging.
However, he will not stand unaided. He will not attempt independent movement. He loves walking aided between people and during lockdown we have been walking him between DH and I and letting him go so he takes a few unaided steps (or falls into our arms). We try to encourage standing unaided but as soon as we stand him up he sits down (doesn't fall but lowers himself). When we walk with him around the house and we let go of one hand, he purposefully sits down.
I'm desperate to make the most of this opportunity in lockdown to focus on his development and all of his peers are now further along than him. How can I encourage DS to stand unaided? I know he won't walk until he gets this nailed. We heap praise on him for the steps he takes which he loves.