I think 4 months was when Hannah started waking up during the night again. I did try her with a bit of baby rice but she wasn't too interested so I just fed her more often. She still hasn't gone back to sleeping at night, she's started solids 2 weeks ago, loves it and thumps the table until she gets fed more, but her sleeping is worse than ever

I'm hoping she starts to settle down soon.
Sorry I can't help other than to say I'm still in the same situation. You could offer him a bit of baby rice and see what he does, if he's not ready he won't be interested in it.
I was looking info up last night about sleeping and the article mentioned that around 4 months babies take more of an interest in what is happening around them so they may not feed as much during the day as they should, and so will make up for it at night. I do think this is true with Hannah as she always wants to see what Matthew is doing and gets distracted from feeding. Maybe its true for Fraser as well?
Debs