Similar to EJ - DD 26 months when DS arrived - and I also wanted to help avoid jealousy issues. I do feel I put through DS alot of stuff that DD didn't have to put up with (e.g. her efforts at helping bathe him etc) but he just adores her - if she is in the room he doesn't look anywhere else so that does make me feel a bit better. She isn't allowed to pick him up and I am always supervising but I do let her have a fair bit of hands on contact with him, and always explain what she is and isn't allowed to do and why. I must use the phrase "He is not a toy" a fair bit because she has said that to me a couple of times. The main problem is she likes to be so close to him I have to pay close attention that she isn't squashing him - but in the main she is very good. I would think with 4-5 year olds there are a few things they can help with in terms of dressing maybe not putting things over the head but putting socks on bubs for example could be a help, or placing a hat on head (my DD is ok at doing this and is 2.5), wiping gently with a flannel etc. I think they will surprise you how good they can be with your little one.