I'm beyond this stage now but my advice is to assess how much you think you can reasonably get done during the working day and have a grown-up, sensible chat with your DP about what this would look like and how any leftover chores will get done.
The word reasonable is really important here. Babies and toddlers have different temperaments and have different nap requirements. If you have a baby that won't be put down, a clingy and needy toddler that never sleeps or a baby that won't nap without being pushed in a buggy then this is a whole different ball game to those with babies and toddlers that are more easy going and sleep in their cots for extended periods in the day. Do not underestimate how different people's parenting experiences can be even if on paper the amount of children/ages can look similar to your's.
Also people have different approaches to the kind of experiences and enrichment they want to give their children. Sure, you could theoretically stay at home all day focussing on chores but is that what you or your partner want for your children? There are baby groups, play groups, playdates, trips to museums, the library, the park, the list really is endless. Just being at home and giving your child your undivided attention is so valuable and toddlers in particular get so much from socialisation and experiencing different things. Put it this way, babies and toddlers in childcare at childminders and nurseries aren't expected to play second fiddle to someone constantly doing domestic chores so why should your children? A balance needs to be struck somewhere for sure, but I believe the priority should be the children not the housework.
In conclusion, you're an adult who knows your children best and can agree with your partner what kind of activities and experiences you want to give your children. You can work out how many hours you have in the working day and how many of those you can devote to chores. Have a proper rational conversation about this with your DP and talk them through everything and agree how to manage leftover tasks. Don't be pressured into trying to do everything or be treated as a lesser partner because you're at home. You're a SAHP not a skivvy.