4 year old acting like a baby and making baby noises

[handsoftime]

My DS is now 4.5 his little sister has just turned 1. He acts like her though, like a baby. She is walking and he'll spend a good chunk of the day crawling about. He'll make baby noises and refuses to talk, just points at stuff. I give him lots of attention too. When his sister is asleep he gets my full focus and we do something together. He has started school so pre- holidays he's only done this on
Weekends. Generally on school
days he's been fine. I've tried ignoring it, saying don't copy your sister, saying act like a big boy, l love you being grown up or being 4. I've even said we should be showing his sister how to act and talk as she wants to be like you. I don't particularly push him
to do anything he wouldn't of done. Things like wiping his bottom on the toilet I feel are age appropriate, so I don't think I'm pushing him to grown up because I'm busy with his sister. My DH works away and is not here much. Anyone experienced this?

Bump for the evening

I think this is fairly normal. Does he do it all the time? DS (nearly 5) does this occasionally (Dd is 10 months). I just say 'oh are you being a baby now' and go along with the imaginative play till he gets bored of it.

I think this is completely normal. My 4 year old does it too. I think it's a fun game (fun for her - I don't love it) and a good way for her to get my attention. I go along with it. Maybe she needs to feel she can be a baby sometimes.