??? Age to put baby in low seat

[feeb]

Just wondering what age have people put baby in removable seat on bottom. On Phil and Ted Dash ??

DS2 doesn't fot in coccoon and seems to be bored lieing flat and not seeing anything apart from me as we wander with pram.

When DS1 has been out of pram in a high chair when out for lunch I have sat DS2 in the seat on top and he loves it but falls to 1 side a bit much still, but he is only there for a short time so not an issue.

So just wondering as also without coccoon makes it a PITA to get him in and out.

Thanks