My little one will soon be 4 month old. Started from two or three weeks ago, he wants to sit up a lot, in the pram, on my laps, then I bought him a Bumbo seat, he loves it. My concern is he s been sitting a lot every day. Almost all his play time, he doesn't like tummy time or lying down... His head is not too firm still. Will sitting up be okay for him? Though it's supported in the pram n on my laps???