Have you tried baby massage? It can help soothe babies and is a wonderful way to bond with your little one.
Use touchy-feely play and simple massage strokes to settle them, focusing on their feet, legs, chest, shoulders, and arms - it'll relax them and clue them in that sleep time is approaching. Massage also stimulates the release of oxytocin, which promotes feelings of relaxation and calmness.
Make sure the room is free from distractions, keep the lights low, and use relaxing baby massage oil to create a soothing environment. You could also try playing some gentle music in the background - this can help set the scene and provide familiarity, especially if you choose songs with a slow rhythm that mirror the calm, soothing movements of your massage.
The routine itself might not be the issue, but what's going on during the day could be disrupting their sleep. Overstimulation is a common culprit - make sure their environment isn't too busy and full of bright colors and loud noises. Instead, create a peaceful space with minimal distractions and lots of calm, quiet time to encourage them to wind down.
Also, consider their diet if they're old enough to eat solids. Some foods like dairy, sugar, and caffeine can overstimulate babies and make it harder for them to relax and settle. You might need to experiment with what they eat during the day to see if anything seems to affect their sleep.
Remember, every baby is different, so don't be afraid to try new things and find what works best for your little one!