The child stands next to the user and looks at him. The user grasps the child by the upper arms and pulls the child up. He supports himself at the same time with one forearm on his lap in order not to lose his balance. When the child is halfway up, the user changes his grip and holds the child with one hand under the child’s bottom and pulls the child up until the child is lying on his stomach on the user’s lap. Then he sits the child up.
Another technique for picking up a child from the floor can be seen at youtube.com/watch (last checked January 2022)