Another vote for Crystal Palace, but we like lunch... I found it difficult to get DS to take a break from all the fun to sit down and eat... but no problem with Crystal Palace since Pooh, Tigger, Piglet and Eeyore are there.
Never been to Chef Mickey's but that's either breakfast or dinner.
For 4 yr olds, Ohana might be a fun character breakfast -- Mickey, Pluto, Lilo, Stitch and you can take the boat to MK after for a fun little boat ride. DS4 enjoyed himself there twice. Food is good, served family style, characters fun. Mickey taught DS how to do the surfing shaka (hang loose) sign.