[roja123]

Could you alter the sentences a little so that you say

I suggest eating now.
I suggest that we eat now.

It could possibly make things a little clearer. You could let them know that the "that" is optional, but it is an indicator that a conjugated verb needs to follow.

Also, not sure if this distinction would complicate things further, but there is a slight difference in that an activity is being suggested in the first sentence and an action in the second. You could highlight this by showing that "I suggest eating now" can be a substitute for
I suggest we eat now.
I suggest you eat now.
I suggest the children eat now.
etc.

Since the sentence with the gerund is suggesting an activity, but not specifying who should do it, you could demonstrate this by doing a comic strip or something where someone makes a gerund suggestion and the wrong person/people takes it up, making for a funny situation. Or maybe a guessing scenario where you have pictures and speech bubbles and the children have to guess who the suggestion would logically be for.

Hope that's a bit helpful!