Earliest date for some liquid food for kittens?

I am worried mom may be running low on milk, and I'm curious if anyone has any suggestions on what the earliest I could expect the kittens to even attempt to intake some food other than from Mom? I would love to feed them kitten glop but they hate the bottle - by 3-4 weeks would they be able to lap it up from a low-sided bowl and/or plate? I'm not planning on depriving them of mom, but she is just so tiny - the kittens are as big as her now and I can't imagine she'll be able to keep making milk for all of them. I am thinking if I regularly feed her kitten glop in a kitten-friendly bowl, they might watch her and try some themselves?

Edited to note I meant the combined kittens were as big as mom.. not individually

I dont think you need to worry too much but you can offer them some kittem glop or simply normal kitten food watered down with warm water or KMR.