My aunt had a clutch of 9 babies and only 4 ate right away. I asked about it and my pal said he only force feeds after 6 weeks or 20% weight loss. Luckily, we only ended up needing to force two. What worked best for us was putting mouse litter in the bin for a couple of days before trying to feed a live hopper mouse. It got them hyped up because of the smell and then they took the food.