DS1 is just 2 & Ds2 is just 10 months, so only a 15 month gap. Ds1 adores his little brother - loves giving him cuddles, kisses, 'helping' him & for the most part will even happily share with him.
In the last couple of weeks though he's started to push him when he's sitting on the floor. Ds2 isn't crawling or standing yet but loves sitting & playing. It's doesn't seem to be done in anger or temper or with any apparent reason for it. He will just randomly walk up to him & push him so he falls backwards.
We've obviously very firmly told him when he's done it that we don't push, you have to be gentle with babies, pushings not nice etc. We've used the naughty step for it to. Ds1 will say to us 'no push ds2' 'fall down, bump head' so he has some understanding. Obviously now we're right next to ds2 when he's on the floor constantly so we can pick him up at the first sign of trouble.
I'm really at a loss as to how to handle this for the best & why he's doing it. Help please?!