Should I wean her?

[Fen Farm Dexters]

We've left our cows to wean their calves naturally for the last three seasons, and they all run together, but one cow calved last night at 9.00pm and when I left her about 10.30pm she was just starting to suckle the new calf. Checked them this morning 6.00am and cow and calf were together and suckling, but at 8.00am had another look and her last year's calf was helping herself. The cow had been booting last years calf away for about the last three weeks. I have separated the herd from the cow and new calf and the new calf is still resting at the moment but looks fine and alert. Do I need to worry and get some more colostrum or will the calf have had or get enough in the next c 12 hours?