I’ve had a few children like this and I find the main issue is jaw height….it’s very difficult to make ‘t’ or ‘d’ with your jaw open/tongue low down.
I therefore have focussed on not only front consonants e.g. L/N/S but also vowels such as ‘ee’ and ‘i’. You can do this in phrases and games and talk about ‘teeth together’ ‘jaw nice and high’… e.g. “need it” “knee” “in” with therapy games.
It’s quite a disordered process and can be tricky to eradicate but thinking and talk about the jaw position for accurate tongue placement can really help.